feat(lang): L4 type checker between parse and emit

selfhost/check/ walks every function, the entry, tests, globals' initializers and
@On listeners with real scopes, and refuses mixed number kinds, text and numbers,
two record types, mismatched slices and fn types, wrong argument counts, wrong
returns and wrong push elements - every mix-up at once, each at its line.
LUDIC_CHECK_REPORT=1 lists them by category. pointer stays untyped (L7's).

What it found is fixed: render3d's HDR scan calling the float-bits extern f_lt
with floats; ludic.shooter's right-stick aim overflowing past half a push;
prof.ludic storing longs in []int; extern arguments now coerced to their
parameters. Text-returning runtime functions say string; Assets.ready says bool.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

LANGUAGE.md

@@ -110,6 +110,35 @@ To move an existing codebase onto modules, build it once with `LUDIC_VIS_REPORT=
 reference that would be refused is printed as `vis: <file>:<line>: <module>.<name> used from
 <file>` and the build goes on, so a script can add the `export`s the program already relies on.
 
+### Types are checked before anything is emitted
+
+Between the parse and the emitter a checker walks every function, the entry, the tests, the
+globals' initializers and every `@On` listener, and refuses a program whose types do not agree -
+all of its mix-ups at once, each at its own line:
+
+```
+trip.ludic:12: error: metres wants an int and this is a float
+trip.ludic:14: error: area takes 2 argument(s) and this call gives 1
+trip.ludic:20: error: + of a string and an int: text joins text only - write string(x) for a number
+3 type error(s)
+```
+
+What it holds apart: `int`, `float`, `fixed` and `bool` (a float or a fixed into an int is
+`int(x)`; a float and a fixed never meet but by a literal, which takes whichever kind its slot is);
+text and numbers (`string(n)` or a template); one record type and another; slices of different
+elements; functions of different types. A call gives exactly as many arguments as there are
+parameters, a `return` gives the declared result, and `push` gives the slice's own element.
+
+`pointer` is untyped, as `void *` is in C: it goes wherever a reference is wanted and takes any
+reference, and a `[]pointer` any slice of references. Restricting what a raw pointer may reach is
+`unsafe`'s job, not the checker's. Bits cross between kinds by name - `as_int(x)` / `as_fixed(n)`
+reinterpret a word, `float_bits(f)` / `float_from_bits(i)` a float's - never by a slot's type.
+
+A name the checker cannot type (an engine namespace's arguments, a query's bindings) agrees with
+everything, so it only ever reports what it can prove; the emitter keeps its own checks behind
+it. `LUDIC_CHECK_REPORT=1` lists every mix-up by category and fails nothing, which is how an
+existing program is measured before it has to pass.
+
 ## Models (entity kinds)
 
 An `model` names a *kind* of entity and the fixed set of properties it

changes/type-checker.md

@@ -0,0 +1,16 @@
+bump: minor
+type: feature
+**A type checker runs before the emitter.** Numbers of different kinds, text and numbers, two
+record types, slices of different elements and functions of different types no longer mix; a call
+with the wrong number of arguments, a `return` of the wrong type and a `push` of the wrong element
+are errors with a line - several of these reached clang as an IR error, or compiled and ran wrong.
+Every mix-up is reported in one run. `pointer` stays untyped. `LUDIC_CHECK_REPORT=1` lists them by
+category without failing.
+
+It found, and this release fixes: render3d's HDR sky scan calling the float-bits extern `f_lt` with
+floats (it passed them in float registers the callee never read); `ludic.shooter`'s right-stick aim
+scaling a fixed deflection by 65536 again, which overflowed past half a push and turned the aim
+round; `prof.ludic` storing longs in an `[]int`; and extern calls, whose arguments are now coerced
+to their parameters like a function's. Runtime functions that return text (`Json.encode`, the
+value, XML, Tiled, HTTP and regex readers, `gl_get_string`) say `string`, and `Assets.ready()`
+says `bool`.

docs/language/assets/assets-ready.md

@@ -4,8 +4,8 @@ name: Assets.ready
 category: assets
 kind: namespace-method
 tokens: Assets.ready
-sig: Assets.ready() -> int
-tip: 1 once every enqueued asset has loaded.
+sig: Assets.ready() -> bool
+tip: true once every enqueued asset has loaded.
 order: 8
 ns: Assets
 member: ready

examples/lang/checked.ludic

@@ -0,0 +1,23 @@
+# checked.ludic — L4: what the checker lets through. A decimal literal is whichever of float and
+# fixed its slot is, an int widens into a float, a string is a pointer, a []string is a
+# []pointer, null is any reference, string(p) says a pointer is text, and a named argument is
+# checked against its own parameter.
+#
+# Running it prints:  7.5 3 12 hi 2 ok
+program Checked {
+  numbers float
+  property Box { w: float = 0.0 }
+  function scale(by: float, n: int) -> float { return by * float(n) }
+  function raw_text() -> pointer { return "hi" }
+  function count(xs: []pointer) -> int { return len(xs) }
+  entry {
+    let f: fixed = 1.5
+    let x: float = 2.5
+    var b: Box = null
+    b = new Box { w: 3 }
+    let p: pointer = "any string"
+    let s: string = string(raw_text())
+    print(`{scale(by: x, n: 3)} {int(b.w)} {int(f * 8)} {s} {count(["a", "b"])} ok`)
+    if p == null { print("none") }
+  }
+}

examples/rejected/every_error.ludic

@@ -0,0 +1,11 @@
+# L4: every mix-up in a program is reported at once, not only the first
+program EveryError {
+  function half(n: int) -> int { return n / 2 }
+  function name() -> int { return "seven" }
+  entry {
+    let on = true
+    print(on + 1)
+    print(half(1, 2))
+    print(name())
+  }
+}

examples/rejected/float_into_int.ludic

@@ -0,0 +1,10 @@
+# L4: a float computed into an int slot is refused - write int(x)
+program FloatIntoInt {
+  numbers float
+  entry {
+    let speed: float = 3.2
+    var metres: int = 0
+    metres = speed * 2.0
+    print(metres)
+  }
+}

examples/rejected/record_as_text.ludic

@@ -0,0 +1,9 @@
+# L4: a record is not text; say which of its fields is meant
+program RecordAsText {
+  property Trail { name: string = "Crater Lake" }
+  function sign(s: string) -> string { return "To " + s }
+  entry {
+    let t = new Trail
+    print(sign(t))
+  }
+}

examples/rejected/record_mixup.ludic

@@ -0,0 +1,10 @@
+# L4: one record is not another, whatever their fields
+program RecordMixup {
+  property Door { open: bool = false }
+  property Key { cut: int = 0 }
+  entry {
+    let k = new Key
+    let d: Door = k
+    print(d.open)
+  }
+}

examples/rejected/text_plus_number.ludic

@@ -0,0 +1,7 @@
+# L4: text joins text only; a number is written with string(n) or a template
+program TextPlusNumber {
+  entry {
+    let n = 3
+    print("apples: " + n)
+  }
+}

examples/rejected/wrong_arity.ludic

@@ -0,0 +1,5 @@
+# L4: a call gives as many arguments as the function has parameters
+program WrongArity {
+  function area(w: int, h: int) -> int { return w * h }
+  entry { print(area(3)) }
+}

packages/ludic.render3d/fmath.ludic

@@ -25,8 +25,6 @@ function fr(n: int, d: int) -> float { return float(n) / float(d) }
 function f_neg1() -> float { return -1.0 }
 function f_clamp(x: float, lo: float, hi: float) -> float { return Math.min(Math.max(x, lo), hi) }
 function f_lerp(a: float, b: float, t: float) -> float { return a + (b - a) * t }
-function f_gt(a: float, b: float) -> bool { return f_lt(b, a) != 0 }
-function f_ls(a: float, b: float) -> bool { return f_lt(a, b) != 0 }
 function f_rad(deg: float) -> float { return deg * (PI / 180.0) }
 function f_fx(x: float) -> fixed { return fixed(x) }
 

packages/ludic.render3d/gltf.ludic

@@ -66,7 +66,7 @@ function gltf_mat_remember(name: string, diff: int, nrm: int, arm: int) -> void
 }
 
 var gltf_cutout: bool = false     # the material being loaded is alpha-blended (a cut-out atlas)
-function gltf_texture(uri: pointer, srgb: bool) -> int {
+function gltf_texture(uri: string, srgb: bool) -> int {
   if gltf_tex_paths == null { gltf_tex_paths = new []pointer;  gltf_tex_ids = words(256) }
   var png: string = uri
   let n = len(uri)
@@ -82,7 +82,7 @@ function gltf_texture(uri: pointer, srgb: bool) -> int {
 }
 
 # the image uri behind materials[m].<slot>.index, or null
-function gltf_mat_uri(mat: Val, slot: pointer) -> pointer {
+function gltf_mat_uri(mat: Val, slot: pointer) -> string {
   var holder = mat
   if slot == "baseColorTexture" or slot == "metallicRoughnessTexture" {
     if value_has(mat, "pbrMetallicRoughness") == 0 { return null }

packages/ludic.render3d/prof.ludic

@@ -201,7 +201,7 @@ function prof_bake_add(us: long) -> void { if prof_on { prof_bake_us_cur = prof_
 function prof_chunk(kind: int, band: int, count: int, us: long) -> void {
   if not prof_on { return }
   if prof_chunk_us == null {
-    prof_chunk_us = new []int;  prof_chunk_kind = new []int
+    prof_chunk_us = new []long;  prof_chunk_kind = new []int
     prof_chunk_band = new []int;  prof_chunk_n = new []int
   }
   push(prof_chunk_us, us);  push(prof_chunk_kind, kind)

packages/ludic.render3d/texture.ludic

@@ -363,9 +363,9 @@ function hdr_decode(path: pointer) -> floats {
         out[o + 1] = Math.min(vg, 60000.0)
         out[o + 2] = Math.min(vb, 60000.0)
         let lum = vr + vg + vb
-        if f_lt(maxl, lum) != 0 { maxl = lum;  hdr_max_x = x;  hdr_max_y = y }
+        if maxl < lum { maxl = lum;  hdr_max_x = x;  hdr_max_y = y }
         if y < h / 2 { skye = skye + Math.min(vg, hdr_clip) * Math.cos((float(y) + 0.5) * dth) * domega }
-        if f_lt(hdr_clip, vg) != 0 or f_lt(hdr_clip, vr) != 0 {
+        if hdr_clip < vg or hdr_clip < vr {
           sr = sr + Math.max(vr - hdr_clip, 0.0) * domega
           sg = sg + Math.max(vg - hdr_clip, 0.0) * domega
           sb = sb + Math.max(vb - hdr_clip, 0.0) * domega

packages/ludic.shooter/shooter.ludic

@@ -417,7 +417,7 @@ function sh_half_w(e: int) -> int {
     if mode == AimMode.RightStick {
       let ax = Input.pad_axis(0, STICK_RIGHT_X)
       let ay = Input.pad_axis(0, STICK_RIGHT_Y)
-      if (ax != 0) or (ay != 0) { target = sh_dir_angle(ax, ay);  have = 1 }
+      if (ax != 0) or (ay != 0) { target = sh_dir_angle_fx(ax, ay);  have = 1 }
     }
     if mode == AimMode.MoveDirection {              # from the movement intent
       let wx = td_get(e, "want_x")
@@ -473,6 +473,12 @@ function sh_dir_angle(dx: int, dy: int) -> int {
   let r = Math.atan2(fixed(dy), fixed(dx))
   return sh_wrap_deg(floor(Math.rad_to_deg(r)))
 }
+# a stick's deflection is already fixed: fixed(dy) on it would scale it by 65536 again and
+# overflow past half a push, turning the aim round
+function sh_dir_angle_fx(dx: fixed, dy: fixed) -> int {
+  let r = Math.atan2(dy, dx)
+  return sh_wrap_deg(floor(Math.rad_to_deg(r)))
+}
 function sh_wrap_deg(d: int) -> int {
   var a = d
   while a < 0 { a += 360 }
@@ -494,8 +500,9 @@ function sh_spawn_bullet(owner: int, fac: int, px: int, py: int, deg: int, speed
   pos_set(b, "x", px)
   pos_set(b, "y", py)
   let rad = Angle.from_degrees(fixed(deg))
-  pr_set(b, "vx", Angle.cos(rad) * fixed(speed))
-  pr_set(b, "vy", Angle.sin(rad) * fixed(speed))
+  # World.set stores a field's raw word: a fixed field is handed its bits by name
+  pr_set(b, "vx", as_int(Angle.cos(rad) * fixed(speed)))
+  pr_set(b, "vy", as_int(Angle.sin(rad) * fixed(speed)))
   pr_set(b, "dir", deg)
   pr_set(b, "speed", speed)
   pr_set(b, "damage", dmg)
@@ -621,8 +628,8 @@ function sh_fire(owner: int, id: int) -> void {
         let rad = Angle.from_degrees(fixed(na))
         let nvx = Angle.cos(rad) * fixed(sp)
         let nvy = Angle.sin(rad) * fixed(sp)
-        pr_set(e, "vx", nvx)
-        pr_set(e, "vy", nvy)
+        pr_set(e, "vx", as_int(nvx))
+        pr_set(e, "vy", as_int(nvy))
       }
     }
     # integrate (Q16.16 with subpixel remainder)

runtime/native/atlas.ludic

@@ -398,7 +398,7 @@ function assets_font(name: pointer) -> int {
 
 function assets_total()  -> int { atlas_init();  return at_q_n }
 function assets_loaded() -> int { atlas_init();  return at_q_pos }
-function assets_ready()  -> int { atlas_init();  if at_q_pos >= at_q_n { return 1 };  return 0 }
+function assets_ready()  -> bool { atlas_init();  return at_q_pos >= at_q_n }
 
 # loading progress as a whole-number percent (0..100); an empty queue is 100.
 function assets_progress() -> int {

runtime/native/base64.ludic

@@ -62,7 +62,7 @@ function base64_decode(src: pointer) -> pointer {
 }
 
 # encode the bytes of NUL-terminated `src` as standard base64 (with '=' padding).
-function base64_encode(src: pointer) -> pointer {
+function base64_encode(src: pointer) -> string {
   let tab = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
   let n = len(src)
   var out = ""

runtime/native/bignum.ludic

@@ -279,7 +279,7 @@ function bigint_to_int(a: BigNum) -> int {
 }
 
 # a limb (< 1e9) as exactly nine digits, left-padded with zeros
-function bn_pad9(x: int) -> pointer {
+function bn_pad9(x: int) -> string {
   var s = string(x)
   var pad = 9 - len(s)
   var out = ""
@@ -287,7 +287,7 @@ function bn_pad9(x: int) -> pointer {
   return out + s
 }
 
-function bigint_str(a: BigNum) -> pointer {
+function bigint_str(a: BigNum) -> string {
   if a.sign == 0 { return "0" }
   var out = ""
   if a.sign < 0 { out = "-" }
@@ -364,7 +364,7 @@ function decimal_rescale(d: Dec, places: int) -> Dec {
   return dec_make(m, places)
 }
 
-function decimal_str(d: Dec) -> pointer {
+function decimal_str(d: Dec) -> string {
   var neg = ""
   var m = d.m
   if m.sign < 0 { neg = "-";  m = bigint_neg(m) }

runtime/native/gl_api.ludic

@@ -946,7 +946,7 @@ extern function gl_get_doublev(pname: int, params: pointer) = "lgl_GetDoublev"
 extern function gl_get_error() -> int = "lgl_GetError"
 extern function gl_get_floatv(pname: int, params: pointer) = "lgl_GetFloatv"
 extern function gl_get_integerv(pname: int, params: pointer) = "lgl_GetIntegerv"
-extern function gl_get_string(name: int) -> pointer = "lgl_GetString"
+extern function gl_get_string(name: int) -> string = "lgl_GetString"
 extern function gl_get_tex_image(target: int, level: int, format: int, type: int, pixels: pointer) = "lgl_GetTexImage"
 extern function gl_get_tex_parameterfv(target: int, pname: int, params: pointer) = "lgl_GetTexParameterfv"
 extern function gl_get_tex_parameteriv(target: int, pname: int, params: pointer) = "lgl_GetTexParameteriv"
@@ -1165,7 +1165,7 @@ extern function gl_clear_bufferiv(buffer: int, drawbuffer: int, value: pointer)
 extern function gl_clear_bufferuiv(buffer: int, drawbuffer: int, value: pointer) = "lgl_ClearBufferuiv"
 extern function gl_clear_bufferfv(buffer: int, drawbuffer: int, value: pointer) = "lgl_ClearBufferfv"
 extern function gl_clear_bufferfi(buffer: int, drawbuffer: int, depth: fixed, stencil: int) = "lgl_ClearBufferfi"
-extern function gl_get_stringi(name: int, index: int) -> pointer = "lgl_GetStringi"
+extern function gl_get_stringi(name: int, index: int) -> string = "lgl_GetStringi"
 extern function gl_draw_arrays_instanced(mode: int, first: int, count: int, instancecount: int) = "lgl_DrawArraysInstanced"
 extern function gl_draw_elements_instanced(mode: int, count: int, type: int, indices: pointer, instancecount: int) = "lgl_DrawElementsInstanced"
 extern function gl_tex_buffer(target: int, internalformat: int, buffer: int) = "lgl_TexBuffer"

runtime/native/http.ludic

@@ -235,7 +235,7 @@ function http_ok(h: int) -> bool {
   return (st >= 200) and (st < 300)
 }
 
-function http_text(h: int) -> pointer {
+function http_text(h: int) -> string {
   if not http_valid(h) { return null }
   return h_body[h - 1]
 }
@@ -245,7 +245,7 @@ function http_body_len(h: int) -> int {
   return h_blen[h - 1]
 }
 
-function http_header_of(h: int, name: pointer) -> pointer {
+function http_header_of(h: int, name: pointer) -> string {
   if not http_valid(h) { return null }
   let s = h - 1
   if h_native[s] == 1 { return hs_header(s, name) }
@@ -332,7 +332,7 @@ function http_parse(resp: pointer, len: int) -> int {
 
 # Look up a header value in a raw header block (case-insensitive), returning a
 # fresh NUL-terminated copy, or null if absent. Lines are "Name: value\r\n".
-function http_find_header(hdr: pointer, name: pointer) -> pointer {
+function http_find_header(hdr: pointer, name: pointer) -> string {
   if hdr == null { return null }
   let nlen = http_cstr_len(name)
   let hlen = http_cstr_len(hdr)

runtime/native/regex_vm.ludic

@@ -150,7 +150,7 @@ function regex_end(m: Match, n: int) -> int {
   if m == null or n < 0 or n > m.ng { return -1 }
   return m.caps[2 * n + 1]
 }
-function regex_group(m: Match, n: int) -> pointer {
+function regex_group(m: Match, n: int) -> string {
   if m == null or n < 0 or n > m.ng { return "" }
   let a = m.caps[2 * n]
   let b = m.caps[2 * n + 1]
@@ -169,7 +169,7 @@ function rx_append(out: IVec, s: pointer, a: int, b: int) -> void {
   var i = a
   while i < b { iv_push(out, s[i] & 255);  i += 1 }
 }
-function regex_replace(str: pointer, pattern: pointer, repl: pointer) -> pointer {
+function regex_replace(str: pointer, pattern: pointer, repl: pointer) -> string {
   let p = regex_compile(pattern)
   if p == null { return str }
   let n = rx_slen(str)

runtime/native/tiled.ludic

@@ -647,7 +647,7 @@ function tmap_resolve(m: Tmap, gid: int) -> GidInfo {
 function tmap_width(m: Tmap) -> int { return m.w }
 function tmap_height(m: Tmap) -> int { return m.h }
 function tmap_layer_count(m: Tmap) -> int { return len(m.layers) }
-function tmap_layer_name(m: Tmap, i: int) -> pointer {
+function tmap_layer_name(m: Tmap, i: int) -> string {
   if i < 0 or i >= len(m.layers) { return "" }
   if m.layers[i].name == null { return "" }
   return m.layers[i].name
@@ -855,7 +855,7 @@ function tmap_tileset_from_value(tv: Val) -> TmTileset {
   return ts
 }
 
-function tiled_join(a: pointer, b: pointer) -> pointer { return Path.normalize(Path.join(a, b)) }
+function tiled_join(a: pointer, b: pointer) -> string { return Path.normalize(Path.join(a, b)) }
 
 # build the runtime map from an intermediate tree, resolving external tilesets
 # and loading tileset images relative to `basedir`.
@@ -1105,7 +1105,7 @@ function tmap_object(m: Tmap, layer: int, i: int) -> Val {
 
 # the shape of an object: "tile" (a gid object), "point", "ellipse", "polygon",
 # "polyline", "text", or "rectangle" (the default).
-function tiled_object_shape(obj: Val) -> pointer {
+function tiled_object_shape(obj: Val) -> string {
   if value_has(obj, "gid") == 1 { return "tile" }
   if value_has(obj, "point") == 1 { return "point" }
   if value_has(obj, "ellipse") == 1 { return "ellipse" }
@@ -1132,7 +1132,7 @@ function tiled_prop_node(container: Val, name: pointer) -> Val {
 
 # a property's raw string value, with a fallback to the object's custom-type
 # default (objecttypes.xml, via the type table). "" when absent everywhere.
-function tiled_prop_str(container: Val, name: pointer) -> pointer {
+function tiled_prop_str(container: Val, name: pointer) -> string {
   let p = tiled_prop_node(container, name)
   if value_kind(p) == 6 { return value_as_str(value_get(p, "value")) }
   # fall back to the container's class default
@@ -1153,7 +1153,7 @@ function tiled_prop_int(container: Val, name: pointer) -> int {
   return xml_atoi(s)
 }
 
-function tiled_prop_type(container: Val, name: pointer) -> pointer {
+function tiled_prop_type(container: Val, name: pointer) -> string {
   let p = tiled_prop_node(container, name)
   if value_kind(p) == 6 { return value_as_str(value_get(p, "type")) }
   let cls = value_as_str(value_get(container, "type"))
@@ -1353,13 +1353,13 @@ function tmap_layer_kind(m: Tmap, layer: int) -> int {
   if layer < 0 or layer >= len(m.layers) { return -1 }
   return m.layers[layer].kind
 }
-function tmap_layer_opacity(m: Tmap, layer: int) -> pointer {
+function tmap_layer_opacity(m: Tmap, layer: int) -> string {
   if layer < 0 or layer >= len(m.layers) { return "" }
   let op = value_get(m.layers[layer].data, "opacity")
   if value_kind(op) == 0 { return "1" }
   return value_as_str(op)
 }
-function tmap_layer_tint(m: Tmap, layer: int) -> pointer {
+function tmap_layer_tint(m: Tmap, layer: int) -> string {
   if layer < 0 or layer >= len(m.layers) { return "" }
   return value_as_str(value_get(m.layers[layer].data, "tintcolor"))
 }

runtime/native/value.ludic

@@ -54,12 +54,12 @@ function value_put(obj: Val, key: pointer, item: Val) -> Val {
 function value_kind(v: Val) -> int { return v.tag }
 function value_count(v: Val) -> int { return len(v.kids) }
 function value_as_int(v: Val) -> int { return v.num }
-function value_as_str(v: Val) -> pointer { if v.txt == null { return "" };  return v.txt }
+function value_as_str(v: Val) -> string { if v.txt == null { return "" };  return v.txt }
 function value_at(list: Val, i: int) -> Val {
   if i < 0 or i >= len(list.kids) { return value_null() }
   return list.kids[i]
 }
-function value_key_at(obj: Val, i: int) -> pointer {
+function value_key_at(obj: Val, i: int) -> string {
   if i < 0 or i >= len(obj.keys) { return "" }
   return obj.keys[i]
 }
@@ -76,7 +76,7 @@ function value_has(obj: Val, key: pointer) -> int {
 
 # --- JSON encode ------------------------------------------------------------
 # escape a string's `"` `\` and newline, wrapping it in quotes.
-function json_quote(s: pointer) -> pointer {
+function json_quote(s: pointer) -> string {
   var out = "\""
   var i = 0
   let n = len(s)
@@ -96,7 +96,7 @@ function json_quote(s: pointer) -> pointer {
 # remainder hits zero. This is the exact inverse of jp_number's fixed decode, so
 # a value_fixed round-trips through JSON bit-for-bit; short values (0.5, 2.0) stay
 # short. Each step keeps frac < 655360, well within i32.
-function json_fixed_str(raw: int) -> pointer {
+function json_fixed_str(raw: int) -> string {
   var a = raw
   var sign = ""
   if a < 0 { sign = "-";  a = -a }
@@ -112,7 +112,7 @@ function json_fixed_str(raw: int) -> pointer {
   return sign + string(ip) + "." + fs
 }
 
-function json_encode(v: Val) -> pointer {
+function json_encode(v: Val) -> string {
   if v.tag == 0 { return "null" }
   if v.tag == 1 { return string(v.num) }
   if v.tag == 2 { return json_fixed_str(v.num) }
@@ -172,7 +172,7 @@ function jp_value(p: JP) -> Val {
 }
 
 # read a quoted string (cursor on the opening quote) -> the unescaped contents.
-function jp_string(p: JP) -> pointer {
+function jp_string(p: JP) -> string {
   p.i += 1                                    # skip opening quote
   var out = ""
   while p.i < p.n {

runtime/native/xml.ludic

@@ -34,8 +34,8 @@ function xml_new(tag: pointer) -> Xml {
 }
 
 # --- accessors --------------------------------------------------------------
-function xml_tag(n: Xml) -> pointer { if n.tag == null { return "" };  return n.tag }
-function xml_text(n: Xml) -> pointer { if n.text == null { return "" };  return n.text }
+function xml_tag(n: Xml) -> string { if n.tag == null { return "" };  return n.tag }
+function xml_text(n: Xml) -> string { if n.text == null { return "" };  return n.text }
 function xml_child_count(n: Xml) -> int { return len(n.kids) }
 function xml_child(n: Xml, i: int) -> Xml {
   if i < 0 or i >= len(n.kids) { return xml_new("") }
@@ -47,7 +47,7 @@ function xml_has(n: Xml, key: pointer) -> int {
   while i < len(n.akeys) { if n.akeys[i] == key { return 1 };  i += 1 }
   return 0
 }
-function xml_attr(n: Xml, key: pointer) -> pointer {
+function xml_attr(n: Xml, key: pointer) -> string {
   var i = 0
   while i < len(n.akeys) { if n.akeys[i] == key { return n.avals[i] };  i += 1 }
   return ""
@@ -92,7 +92,7 @@ function xml_atoi(s: pointer) -> int {
 # raw run. Only bytes 0..255 of a character reference are emitted (Ludic strings
 # are byte strings); a code point above that is written as its low byte, which is
 # ample for the ASCII/Latin-1 text Tiled attributes carry.
-function xml_unescape(s: pointer) -> pointer {
+function xml_unescape(s: pointer) -> string {
   # fast path: no '&' means nothing to expand
   var k = 0
   let m = len(s)
@@ -153,7 +153,7 @@ function xml_hexval(c: int) -> int {
 # a one-byte string holding byte value `b` (1..255); "" for 0 (a NUL can't sit in
 # a Ludic string). Built by slicing a 256-byte table of every byte value.
 var xml_bytetab: pointer = null
-function xml_byte(b: int) -> pointer {
+function xml_byte(b: int) -> string {
   if b <= 0 { return "" }
   if xml_bytetab == null {
     let t = bytes(257)
@@ -202,7 +202,7 @@ function xp_skip_misc(p: XP) -> bool {
 }
 
 # read a name (element or attribute): letters, digits, '_', '-', ':', '.'
-function xp_name(p: XP) -> pointer {
+function xp_name(p: XP) -> string {
   let start = p.i
   while p.i < p.n {
     let c = p.s[p.i]

selfhost/backend/emit_call.ludic

@@ -1377,13 +1377,24 @@ function emit_call(e: Node) -> Val {
   let ext = find_extern(name)
   if (ext != null) {
     reorder_named(e, param_labels(ext))
+    # each argument is coerced to its parameter, as a function's are: passed as its own
+    # type, a float given to an int parameter arrived in a float register the callee
+    # never reads, and the callee compared whatever the integer register held
+    let eptys = param_types(ext)
     let eargs = new []pointer
     let eatys = new []pointer
     var ei = 0
-    while ei < len(e.kids) { let v = emit_expr(e.kids[ei]);  push(eargs, v.code);  push(eatys, v.ty);  ei += 1 }
+    while ei < len(e.kids) {
+      let v = emit_expr(e.kids[ei])
+      var pty = v.ty
+      if ei < len(eptys) { pty = eptys[ei] }
+      push(eargs, coerce_code(v, pty))
+      push(eatys, pty)
+      ei += 1
+    }
     let erl = llty(ext.ty)
     emit("  ")
-    var erreg = "0"
+    var erreg: pointer = "0"
     if not (erl == "void") { erreg = nreg();  emit(erreg);  emit(" = ") }
     emit("call ");  emit(erl);  emit(" @");  emit(ext.a.s);  emit("(")
     ei = 0
@@ -1425,7 +1436,7 @@ function emit_call(e: Node) -> Val {
   }
   let rl = llty(fn2.ty)
   emit("  ")
-  var rreg = "0"
+  var rreg: pointer = "0"
   if not (rl == "void") { rreg = nreg();  emit(rreg);  emit(" = ") }
   emit("call ");  emit(rl);  emit(" @fn_");  emit(cname);  emit("(")
   i = 0

selfhost/backend/emit_float.ludic

@@ -168,7 +168,7 @@ function lit_as_fixed(v: Val) -> Val {
 function emit_fp_bin(op: pointer, a: Val, b: Val) -> Val {
   if (a.ty == "fixed") and not (fixed_lit_code(b) == "") { return emit_bin_vals(op, a, lit_as_fixed(b), false) }
   if (b.ty == "fixed") and not (fixed_lit_code(a) == "") { return emit_bin_vals(op, lit_as_fixed(a), b, false) }
-  var t = "float"
+  var t: pointer = "float"
   if is_fp(a.ty) and is_fp(b.ty) { t = fp_result(a.ty, b.ty) }
   else { if is_fp(a.ty) { t = a.ty } else { t = b.ty } }
   let ac = to_fp(a, t, `the left side of {op}`)
@@ -336,7 +336,7 @@ function fp_pick(meth: pointer, t: pointer, x: pointer, y: pointer) -> pointer {
 # the float type a Math call works in, given its already-evaluated first
 # argument and the static types of the rest; "" when it is not a float call
 function fp_math_type(first: Val, e: Node) -> pointer {
-  var t = ""
+  var t: pointer = ""
   if is_fp(first.ty) { t = first.ty }
   var i = 1
   while i < len(e.kids) {

selfhost/backend/emit_fnval.ludic

@@ -79,7 +79,7 @@ function emit_indirect_call(fv: Val, e: Node) -> Val {
   }
   let rl = llty(ret)
   emit("  ")
-  var rreg = "0"
+  var rreg: pointer = "0"
   if not (rl == "void") {
     rreg = nreg()
     emit(rreg)

selfhost/backend/emit_stmt.ludic

@@ -28,8 +28,8 @@ function compound_op(tok: pointer) -> pointer {
 function emit_assign(st: Node) -> void {
   # resolve the target's address and type
   let t = st.a
-  var addr = "0"
-  var ty = "int"
+  var addr: pointer = "0"
+  var ty: pointer = "int"
   if t.kind == E_ID {
     let li = loc_find(t.s)
     if li >= 0 {
@@ -209,7 +209,7 @@ function emit_match_tagged(st: Node, sv: Val, en: Node) -> void {
     let arm = st.kids[i]
     if arm_is_default(arm) { deflt = arm }
     else {
-      var acc = "0"
+      var acc: pointer = "0"
       var first = true
       var bindPat: Node = null
       var p = 0
@@ -262,7 +262,7 @@ function emit_match(st: Node) -> void {
     let arm = st.kids[i]
     if arm_is_default(arm) { deflt = arm }
     else {
-      var acc = "0"
+      var acc: pointer = "0"
       var first = true
       var p = 0
       while p < len(arm.kids) {
@@ -303,7 +303,7 @@ function emit_emit(st: Node) -> Val {
     var j = 0
     while j < len(st.a.kids) { if (st.a.kids[j].s == fd.s) { av = st.a.kids[j].a };  j += 1 }
     let lt = llty(fd.ty)
-    var code = "0"
+    var code: pointer = "0"
     if (lt == "ptr") { code = "null" }
     if (av != null) { let v = emit_expr(av);  code = v.code }
     else { if (fd.a != null) { let dv = emit_expr(fd.a);  code = dv.code } }   # declared default

selfhost/backend/game/emit_machine.ludic

@@ -30,7 +30,7 @@ function machine_state_value(m: Node, state: Node) -> pointer {
 
 function emit_machine(st: Node) -> void {
   let gv = machine_var(st.a)
-  var s = ""
+  var s: pointer = ""
   if (gv != null) { s = emit_bind(`load i32, ptr @g_{st.a.s}`) }
   else {
     let regv = emit_expr(st.a)

selfhost/backend/game/emit_query.ludic

@@ -38,7 +38,7 @@ function emit_query(st: Node) -> void {
   while t < len(terms.kids) {
     let tm = terms.kids[t]
     let ak = find_arch_id(tm.s)
-    var ok = "0"
+    var ok: pointer = "0"
     if ak > 0 {
       let kp = nreg();  emit("  ");  emit(kp);  emit(" = getelementptr inbounds [");  emit(me);  emit(" x i32], ptr @L_kind, i32 0, i32 ");  emit(i1);  emit("\n")
       let kv = emit_bind(`load i32, ptr {kp}`)

selfhost/check/check_call.ludic

@@ -0,0 +1,150 @@
+# check_call.ludic — L4: a call gives each parameter the type it asks for, and as many arguments
+# as there are parameters. A function, an extern, a function value (a local, a global or a
+# record's field) and the builtins that convert are checked; a namespace call (Input.pad_axis)
+# gives the result type of the Ludic function behind it, and its arguments are the emitter's.
+function ck_params(f: Node, labels: []pointer, tys: []pointer) -> void {
+  var i = 0
+  while i < len(f.kids) {
+    if f.kids[i].kind == N_PARAM {
+      push(labels, f.kids[i].s)
+      push(tys, f.kids[i].ty)
+    }
+    i += 1
+  }
+}
+function ck_call_fn(e: Node, name: pointer, f: Node) -> pointer {
+  let labels = new []pointer
+  let tys = new []pointer
+  ck_params(f, labels, tys)
+  ck_args(e, name, labels, tys)
+  if f.ty == null { return "void" }
+  return f.ty
+}
+function ck_call_sig(e: Node, name: pointer, t: pointer) -> pointer {
+  ck_args(e, name, new []pointer, fn_ty_params(t))
+  return fn_ty_ret(t)
+}
+function ck_label_at(labels: []pointer, s: pointer) -> int {
+  var i = 0
+  while i < len(labels) {
+    if labels[i] == s { return i }
+    i += 1
+  }
+  return -1
+}
+function ck_args(e: Node, name: pointer, labels: []pointer, tys: []pointer) -> void {
+  let n = len(e.kids)
+  if n > 0 and e.kids[0].kind == E_FINIT {
+    var j = 0
+    while j < n {
+      let fi = e.kids[j]
+      let vt = ck_expr(fi.a)
+      let at = ck_label_at(labels, fi.s)
+      if at >= 0 { ck_give(tys[at], vt, fi.a, `argument {fi.s} of {name}`) }
+      j += 1
+    }
+    return
+  }
+  if n != len(tys) { ck_err("arity", e, `{name} takes {itoa(len(tys))} argument(s) and this call gives {itoa(n)}`) }
+  var i = 0
+  while i < n {
+    let at = ck_expr(e.kids[i])
+    if i < len(tys) { ck_give(tys[i], at, e.kids[i], `argument {itoa(i + 1)} of {name}`) }
+    i += 1
+  }
+}
+function ck_walk_args(e: Node) -> void {
+  var i = 0
+  while i < len(e.kids) {
+    ck_any(e.kids[i])
+    i += 1
+  }
+}
+# the builtins whose type is their name, and push, whose element must fit the slice
+function ck_builtin(e: Node, name: pointer) -> pointer {
+  if (name == "string") or (name == "int") or (name == "float") or (name == "fixed") or (name == "long") or (name == "double") {
+    ck_walk_args(e)
+    return name
+  }
+  if (name == "as_int") or (name == "as_fixed") {
+    ck_walk_args(e)
+    return name[3..len(name)]
+  }
+  if (name == "len") or (name == "float_bits") {
+    ck_walk_args(e)
+    return "int"
+  }
+  if (name == "float_from_bits") {
+    ck_walk_args(e)
+    return "float"
+  }
+  if (name == "print") {
+    ck_walk_args(e)
+    return "void"
+  }
+  if (name == "push") and len(e.kids) == 2 {
+    let st = ck_expr(e.kids[0])
+    let vt = ck_expr(e.kids[1])
+    if not ck_unknown(st) and is_slice_ty(st) { ck_give(slice_elem(st), vt, e.kids[1], `push onto {ck_a(st)}`) }
+    return "void"
+  }
+  return null
+}
+function ck_call(e: Node) -> pointer {
+  let c = e.a
+  if c.kind == E_ID { return ck_call_named(e, c.s) }
+  if c.kind == E_MEMBER {
+    let b = c.a
+    if b.kind == E_ID and ck_local(b.s) < 0 and ck_global(b.s) == null {
+      # Ns.fn: the emitter's own table lowers it, supplying defaults and reordering, so the
+      # Ludic function behind it gives the result's type and nothing about the arguments
+      ck_walk_args(e)
+      let nf = ck_fn(ns_lower(b.s) + "_" + c.s)
+      if nf != null and nf.ty != null { return nf.ty }
+      return "?"
+    }
+    let r = ck_record(ck_expr(b))
+    if r != null {
+      let ft = ck_field(r, c.s)
+      if ft != null and is_fn_type(ft) { return ck_call_sig(e, c.s, ft) }
+    }
+    ck_walk_args(e)
+    return "?"
+  }
+  ck_expr(c)
+  ck_walk_args(e)
+  return "?"
+}
+function ck_call_named(e: Node, name: pointer) -> pointer {
+  let li = ck_local(name)
+  if li >= 0 {
+    if is_fn_type(ck_tys[li]) { return ck_call_sig(e, name, ck_tys[li]) }
+    ck_walk_args(e)
+    return "?"
+  }
+  let bt = ck_builtin(e, name)
+  if bt != null { return bt }
+  let f = ck_fn(name)
+  if f != null { return ck_call_fn(e, name, f) }
+  let x = ck_extern(name)
+  if x != null { return ck_call_fn(e, name, x) }
+  let g = ck_global(name)
+  if g != null and is_fn_type(g.ty) { return ck_call_sig(e, name, g.ty) }
+  ck_walk_args(e)
+  return "?"
+}
+# emit E(field: v): each field gets the type the event declares for it
+function ck_emit(s: Node) -> void {
+  let ev = find_event(s.s)
+  if s.a == null { return }
+  var i = 0
+  while i < len(s.a.kids) {
+    let fi = s.a.kids[i]
+    let vt = ck_expr(fi.a)
+    if ev != null {
+      let ft = ck_field(ev, fi.s)
+      if ft != null { ck_give(ft, vt, fi.a, `field {fi.s} of {s.s}`) }
+    }
+    i += 1
+  }
+}

selfhost/check/check_env.ludic

@@ -0,0 +1,57 @@
+# check_env.ludic — L4: the checker's scopes and its errors. A scope is a mark in one list of
+# (name, type) pairs; a lookup walks it from the end, so an inner name hides an outer one.
+var ck_names: []pointer = new []pointer
+var ck_tys: []pointer = new []pointer
+var ck_ret: pointer = "void"            # the result type of the function being checked
+var ck_errors: int = 0
+var ck_report: int = -1                 # LUDIC_CHECK_REPORT=1: list every mix-up by category, fail nothing
+
+var ck_top: int = 0                     # the scope stack's height; the lists only grow
+function ck_bind(name: pointer, ty: pointer) -> void {
+  var t = ty
+  if (t == "null") or t == null { t = "?" }
+  if ck_top < len(ck_names) {
+    ck_names[ck_top] = name
+    ck_tys[ck_top] = t
+  } else {
+    push(ck_names, name)
+    push(ck_tys, t)
+  }
+  ck_top += 1
+}
+function ck_mark() -> int { return ck_top }
+function ck_pop(m: int) -> void { ck_top = m }
+function ck_local(name: pointer) -> int {
+  var i = ck_top - 1
+  while i >= 0 {
+    if ck_names[i] == name { return i }
+    i -= 1
+  }
+  return -1
+}
+function ck_reporting() -> bool {
+  if ck_report < 0 {
+    ck_report = 0
+    if getenv("LUDIC_CHECK_REPORT") != null { ck_report = 1 }
+  }
+  return ck_report == 1
+}
+# every mix-up is reported, not only the first: a type change shows everything it breaks at once
+function ck_err(cat: pointer, n: Node, msg: pointer) -> void {
+  var file: pointer = ""
+  var line = 0
+  if n != null {
+    if n.file != null { file = n.file }
+    line = n.line
+  }
+  var m = `{file}:{itoa(line)}: error: {msg}\n`
+  if ck_reporting() { m = `check[{cat}]: {file}:{itoa(line)}: {msg}\n` }
+  file_write(file_stderr(), m, len(m))
+  ck_errors += 1
+}
+# a value given where a type is wanted: `what` says where ("argument 2 of f", "x")
+function ck_give(to: pointer, from: pointer, e: Node, what: pointer) -> void {
+  let cat = ck_mismatch(to, from, e)
+  if cat == null { return }
+  ck_err(cat, e, `{what} wants {ck_a(to)} and this is {ck_a(from)}`)
+}

selfhost/check/check_expr.ludic

@@ -0,0 +1,132 @@
+# check_expr.ludic — L4: the type of an expression, and every mix-up inside it. Each form works
+# out its operands' types first, so an error deep in an argument is found as well as one at the top.
+function ck_field(r: Node, name: pointer) -> pointer {
+  var i = 0
+  while i < len(r.kids) {
+    if (r.kids[i].s == name) { return r.kids[i].ty }
+    i += 1
+  }
+  return null
+}
+# anything the checker does not type is still walked for the errors inside it
+function ck_walk(e: Node) -> void {
+  if e == null { return }
+  ck_any(e.a)
+  ck_any(e.b)
+  ck_any(e.c)
+  var i = 0
+  while i < len(e.kids) {
+    ck_any(e.kids[i])
+    i += 1
+  }
+}
+function ck_any(n: Node) -> void {
+  if n == null { return }
+  if n.kind == N_BLOCK { ck_block(n);  return }
+  if n.kind == E_FINIT { ck_expr(n.a);  return }
+  if (n.kind >= S_LET and n.kind <= S_BECOME) or n.kind == S_EMIT { ck_stmt(n);  return }
+  ck_expr(n)
+}
+function ck_expr(e: Node) -> pointer {
+  if e == null { return "?" }
+  let k = e.kind
+  if k == E_INT { return "int" }
+  if k == E_FLOAT {
+    if is_float_file(e.file) { return "float" }
+    return "fixed"
+  }
+  if k == E_STR { return "string" }
+  if k == E_SLICE { ck_walk(e);  return "string" }
+  if k == E_BOOL { return "bool" }
+  if k == E_NULL { return "null" }
+  if k == E_ID { return ck_id(e) }
+  if k == E_FNREF {
+    let f = ck_fn(e.s)
+    if f != null { return fn_sig_of(f) }
+    return "?"
+  }
+  if k == E_NEW { return ck_new(e) }
+  if k == E_LIST { return ck_list(e) }
+  if k == E_BIN { return ck_bin(e) }
+  if k == E_UN { return ck_un(e) }
+  if k == E_MEMBER { return ck_member(e) }
+  if k == E_INDEX { return ck_index_of(e) }
+  if k == E_CALL { return ck_call(e) }
+  if k == S_EMIT { ck_emit(e);  return "?" }
+  ck_walk(e)
+  return "?"
+}
+function ck_id(e: Node) -> pointer {
+  let li = ck_local(e.s)
+  if li >= 0 { return ck_tys[li] }
+  let g = ck_global(e.s)
+  if g != null { return g.ty }
+  return "?"
+}
+function ck_new(e: Node) -> pointer {
+  let r = ck_record(e.s)
+  if e.a != null {
+    var i = 0
+    while i < len(e.a.kids) {
+      let fi = e.a.kids[i]
+      let vt = ck_expr(fi.a)
+      if r != null and fi.kind == E_FINIT {
+        let ft = ck_field(r, fi.s)
+        if ft != null { ck_give(ft, vt, fi.a, `field {fi.s} of {e.s}`) }
+      }
+      i += 1
+    }
+  }
+  return e.s
+}
+function ck_list(e: Node) -> pointer {
+  var t: pointer = "?"
+  var i = 0
+  while i < len(e.kids) {
+    let et = ck_expr(e.kids[i])
+    if ck_unknown(t) { t = et }
+    else { ck_give(t, et, e.kids[i], `an element of a []{t}`) }
+    i += 1
+  }
+  if ck_unknown(t) or (t == "null") { return "?" }
+  return "[]" + t
+}
+function ck_un(e: Node) -> pointer {
+  let t = ck_expr(e.a)
+  if (e.s == "not") or (e.s == "!") {
+    ck_cond(e.a, t)
+    return "bool"
+  }
+  if (e.s == "-") and (t == "bool") { ck_err("bool", e, "- on a bool") }
+  return t
+}
+function ck_member(e: Node) -> pointer {
+  let b = e.a
+  if b.kind == E_ID and ck_local(b.s) < 0 and ck_global(b.s) == null {
+    # a namespace, an enum or a component name: Math.PI, Color.Red, Thing.of
+    let en = ck_enum(b.s)
+    if en != null and not enum_is_tagged(en) { return b.s }
+    return "?"
+  }
+  let bt = ck_expr(b)
+  if ck_unknown(bt) { return "?" }
+  let r = ck_record(bt)
+  if r != null {
+    let ft = ck_field(r, e.s)
+    if ft != null { return ft }
+  }
+  return "?"
+}
+function ck_index_of(e: Node) -> pointer {
+  let bt = ck_expr(e.a)
+  let it = ck_expr(e.b)
+  if not ck_unknown(it) and not ck_is_int(it) { ck_err("index", e.b, `an index wants an int and this is {ck_a(it)}`) }
+  if ck_unknown(bt) { return "?" }
+  if is_slice_ty(bt) { return slice_elem(bt) }
+  if (bt == "string") or (bt == "words") { return "int" }
+  if (bt == "floats") { return "float" }
+  if (bt == "doubles") { return "double" }
+  if (bt == "fixeds") { return "fixed" }
+  if (bt == "pointers") { return "pointer" }
+  return "?"
+}

selfhost/check/check_index.ludic

@@ -0,0 +1,74 @@
+# check_index.ludic — L4: the checker's name index. The emitter finds a declaration by scanning
+# every one (find_fn, find_global, find_comp); a pass that asks about every call and every name
+# builds a hash of them once instead. One table per kind of declaration.
+const CK_SLOTS: int = 65536
+var ck_fn_k: []pointer = new []pointer
+var ck_fn_v: []Node = new []Node
+var ck_gl_k: []pointer = new []pointer
+var ck_gl_v: []Node = new []Node
+var ck_rec_k: []pointer = new []pointer
+var ck_rec_v: []Node = new []Node
+var ck_en_k: []pointer = new []pointer
+var ck_en_v: []Node = new []Node
+var ck_ex_k: []pointer = new []pointer
+var ck_ex_v: []Node = new []Node
+
+function ck_hash(s: pointer) -> int {
+  var h = 5381
+  var i = 0
+  let n = len(s)
+  while i < n {
+    h = (h * 33 + s[i]) % 1000003
+    i += 1
+  }
+  return h % CK_SLOTS
+}
+function ck_tab_init(k: []pointer, v: []Node) -> void {
+  var i = 0
+  while i < CK_SLOTS {
+    push(k, null)
+    push(v, null)
+    i += 1
+  }
+}
+# the first declaration of a name wins, as it does in the emitter
+function ck_tab_put(k: []pointer, v: []Node, name: pointer, d: Node) -> void {
+  var h = ck_hash(name)
+  while k[h] != null {
+    if k[h] == name { return }
+    h = (h + 1) % CK_SLOTS
+  }
+  k[h] = name
+  v[h] = d
+}
+function ck_tab_get(k: []pointer, v: []Node, name: pointer) -> Node {
+  if name == null { return null }
+  var h = ck_hash(name)
+  while k[h] != null {
+    if k[h] == name { return v[h] }
+    h = (h + 1) % CK_SLOTS
+  }
+  return null
+}
+function ck_index() -> void {
+  ck_tab_init(ck_fn_k, ck_fn_v)
+  ck_tab_init(ck_gl_k, ck_gl_v)
+  ck_tab_init(ck_rec_k, ck_rec_v)
+  ck_tab_init(ck_en_k, ck_en_v)
+  ck_tab_init(ck_ex_k, ck_ex_v)
+  var i = 0
+  while i < len(prog) {
+    let d = prog[i]
+    if d.kind == N_FN { ck_tab_put(ck_fn_k, ck_fn_v, d.s, d) }
+    if d.kind == N_VAR or d.kind == N_CONST { ck_tab_put(ck_gl_k, ck_gl_v, d.s, d) }
+    if d.kind == N_COMP { ck_tab_put(ck_rec_k, ck_rec_v, d.s, d) }
+    if d.kind == N_ENUM { ck_tab_put(ck_en_k, ck_en_v, d.s, d) }
+    if d.kind == N_EXTERN { ck_tab_put(ck_ex_k, ck_ex_v, d.s, d) }
+    i += 1
+  }
+}
+function ck_fn(name: pointer) -> Node { return ck_tab_get(ck_fn_k, ck_fn_v, name) }
+function ck_global(name: pointer) -> Node { return ck_tab_get(ck_gl_k, ck_gl_v, name) }
+function ck_record(name: pointer) -> Node { return ck_tab_get(ck_rec_k, ck_rec_v, name) }
+function ck_enum(name: pointer) -> Node { return ck_tab_get(ck_en_k, ck_en_v, name) }
+function ck_extern(name: pointer) -> Node { return ck_tab_get(ck_ex_k, ck_ex_v, name) }

selfhost/check/check_ops.ludic

@@ -0,0 +1,84 @@
+# check_ops.ludic — L4: operators. Arithmetic keeps to one kind of number (a float never meets a
+# fixed but by a literal), text joins text only, a bool is not a number, and a comparison is
+# between two things of one class.
+function ck_cond(e: Node, t: pointer) -> void {
+  if ck_unknown(t) or (t == "bool") { return }
+  ck_err("cond", e, `a condition wants a bool and this is {ck_a(t)}`)
+}
+function ck_bin(e: Node) -> pointer {
+  let op = e.s
+  let l = ck_expr(e.a)
+  let r = ck_expr(e.b)
+  return ck_binop(e, op, l, r, e.a, e.b)
+}
+function ck_binop(e: Node, op: pointer, l: pointer, r: pointer, a: Node, b: Node) -> pointer {
+  if (op == "and") or (op == "or") or (op == "&&") or (op == "||") {
+    ck_cond(a, l)
+    ck_cond(b, r)
+    return "bool"
+  }
+  if (op == "==") or (op == "!=") or (op == "<") or (op == ">") or (op == "<=") or (op == ">=") {
+    ck_compare(e, op, l, r, a, b)
+    return "bool"
+  }
+  if (op == "+") or (op == "-") or (op == "*") or (op == "/") or (op == "%") { return ck_arith(e, op, l, r, a, b) }
+  if (op == "&") or (op == "|") or (op == "^") or (op == "<<") or (op == ">>") {
+    if (l == "long") or (r == "long") { return "long" }
+    return "int"
+  }
+  return "?"
+}
+function ck_compare(e: Node, op: pointer, l: pointer, r: pointer, a: Node, b: Node) -> void {
+  if ck_unknown(l) or ck_unknown(r) or (l == "null") or (r == "null") { return }
+  let cl = ck_class(l)
+  let cr = ck_class(r)
+  # a pointer holding text is compared with a string all through the runtime and the compiler
+  if ((l == "pointer") and (cr == "string")) or ((r == "pointer") and (cl == "string")) { return }
+  if cl != cr {
+    ck_err("compare", e, `{op} between {ck_a(l)} and {ck_a(r)}`)
+    return
+  }
+  if ck_is_rec(l) and ck_is_rec(r) and (l != r) { ck_err("compare", e, `{op} between {ck_a(l)} and {ck_a(r)} can never be true`) }
+  if ck_is_lit(a) or ck_is_lit(b) { return }
+  if (l == "fixed") and ck_is_float(r) { ck_err("fixed", e, `{op} between a fixed and {ck_a(r)}`) }
+  if (r == "fixed") and ck_is_float(l) { ck_err("fixed", e, `{op} between {ck_a(l)} and a fixed`) }
+}
+# `string` and the untyped `pointer` are both text to an operator (the emitter's is_textish)
+function ck_is_text(t: pointer) -> bool { return (t == "string") or (t == "pointer") }
+function ck_arith(e: Node, op: pointer, l: pointer, r: pointer, a: Node, b: Node) -> pointer {
+  if ck_is_text(l) or ck_is_text(r) {
+    if ck_unknown(l) or ck_unknown(r) { return "string" }
+    if ck_is_text(l) and ck_is_text(r) and (op == "+") { return "string" }
+    ck_err("text", e, `{op} of {ck_a(l)} and {ck_a(r)}: text joins text only - write string(x) for a number`)
+    return "?"
+  }
+  if ck_unknown(l) or ck_unknown(r) { return "?" }
+  if (l == "bool") or (r == "bool") {
+    ck_err("bool", e, `{op} on a bool`)
+    return "?"
+  }
+  if ck_is_num(l) and ck_is_num(r) { return ck_num_result(e, op, l, r, a, b) }
+  ck_err("kind", e, `{op} of {ck_a(l)} and {ck_a(r)}`)
+  return "?"
+}
+# a decimal literal is whichever of float and fixed the other side is
+function ck_num_result(e: Node, op: pointer, l: pointer, r: pointer, a: Node, b: Node) -> pointer {
+  if (l == "fixed") and ck_is_float(r) {
+    if ck_is_lit(b) { return "fixed" }
+    if ck_is_lit(a) { return r }
+    ck_err("fixed", e, `{op} of a fixed and {ck_a(r)}: convert one with float(x) or fixed(x)`)
+    return "?"
+  }
+  if (r == "fixed") and ck_is_float(l) {
+    if ck_is_lit(a) { return "fixed" }
+    if ck_is_lit(b) { return l }
+    ck_err("fixed", e, `{op} of {ck_a(l)} and a fixed: convert one with float(x) or fixed(x)`)
+    return "?"
+  }
+  if (l == "double") or (r == "double") { return "double" }
+  if ck_is_float(l) { return l }
+  if ck_is_float(r) { return r }
+  if (l == "fixed") or (r == "fixed") { return "fixed" }
+  if (l == "long") or (r == "long") { return "long" }
+  return "int"
+}

selfhost/check/check_stmt.ludic

@@ -0,0 +1,158 @@
+# check_stmt.ludic — L4: statements, and the pass itself. check_program runs between the parse and
+# the emitter over everything the program wrote (not the runtime spliced in after it): every
+# function, the entry, the tests, the globals' initializers and every @On listener with its
+# event's fields in scope. ECS handler, query, spawn and machine bodies bind names the checker
+# does not model, so they are left to the emitter.
+function ck_block(b: Node) -> void {
+  if b == null { return }
+  if b.kind != N_BLOCK {
+    ck_stmt(b)
+    return
+  }
+  let m = ck_mark()
+  var i = 0
+  while i < len(b.kids) {
+    ck_stmt(b.kids[i])
+    i += 1
+  }
+  ck_pop(m)
+}
+function ck_target(t: Node) -> pointer {
+  if t.kind == E_ID { return ck_id(t) }
+  return ck_expr(t)
+}
+function ck_let(s: Node) -> void {
+  var t: pointer = "?"
+  if s.a != null { t = ck_expr(s.a) }
+  if s.ty != null {
+    if s.a != null { ck_give(s.ty, t, s.a, s.s) }
+    ck_bind(s.s, s.ty)
+    return
+  }
+  ck_bind(s.s, t)
+}
+function ck_assign(s: Node) -> void {
+  let lt = ck_target(s.a)
+  let rt = ck_expr(s.b)
+  var what: pointer = "this assignment"
+  if s.a.kind == E_ID { what = s.a.s }
+  if s.a.kind == E_MEMBER { what = `field {s.a.s}` }
+  if (s.s == "=") {
+    ck_give(lt, rt, s.b, what)
+    return
+  }
+  let op = s.s[0..1]
+  let res = ck_binop(s, op, lt, rt, s.a, s.b)
+  ck_give(lt, res, s.b, what)
+}
+function ck_match(s: Node) -> void {
+  ck_expr(s.a)
+  var i = 0
+  while i < len(s.kids) {
+    let arm = s.kids[i]
+    let m = ck_mark()
+    var p = 0
+    while p < len(arm.kids) {
+      let pat = arm.kids[p]
+      # `Door(n) =>` binds its payload's names
+      if pat.kind == E_CALL {
+        var q = 0
+        while q < len(pat.kids) {
+          if pat.kids[q].kind == E_ID { ck_bind(pat.kids[q].s, "?") }
+          q += 1
+        }
+      }
+      p += 1
+    }
+    ck_block(arm.a)
+    ck_pop(m)
+    i += 1
+  }
+}
+function ck_stmt(s: Node) -> void {
+  if s == null { return }
+  let k = s.kind
+  if k == N_BLOCK { ck_block(s);  return }
+  if k == S_LET { ck_let(s);  return }
+  if k == S_ASSIGN { ck_assign(s);  return }
+  if k == S_IF {
+    ck_cond(s.a, ck_expr(s.a))
+    ck_block(s.b)
+    ck_block(s.c)
+    return
+  }
+  if k == S_WHILE {
+    ck_cond(s.a, ck_expr(s.a))
+    ck_block(s.b)
+    return
+  }
+  if k == S_FOR {
+    ck_expr(s.a)
+    ck_expr(s.b)
+    let m = ck_mark()
+    ck_bind(s.s, "int")
+    ck_block(s.c)
+    ck_pop(m)
+    return
+  }
+  if k == S_RETURN {
+    if s.a == null { return }
+    let t = ck_expr(s.a)
+    if (ck_ret != "void") { ck_give(ck_ret, t, s.a, "the result") }
+    return
+  }
+  if k == S_EXPR { ck_expr(s.a);  return }
+  if k == S_MATCH { ck_match(s);  return }
+  if k == S_EMIT { ck_emit(s);  return }
+}
+function ck_fn_body(d: Node) -> void {
+  let m = ck_mark()
+  var i = 0
+  while i < len(d.kids) {
+    if d.kids[i].kind == N_PARAM { ck_bind(d.kids[i].s, d.kids[i].ty) }
+    i += 1
+  }
+  ck_ret = d.ty
+  if ck_ret == null { ck_ret = "void" }
+  ck_block(d.a)
+  ck_ret = "void"
+  ck_pop(m)
+}
+function ck_listener(l: Node) -> void {
+  let ev = find_event(l.s)
+  let m = ck_mark()
+  if ev != null {
+    var i = 0
+    while i < len(ev.kids) {
+      ck_bind(ev.kids[i].s, ev.kids[i].ty)
+      i += 1
+    }
+  }
+  ck_ret = "void"
+  ck_block(l.a)
+  ck_pop(m)
+}
+# LUDIC_CHECK=0 turns the pass off, for bisecting a checker fault; nothing else should need it
+function check_program() -> void {
+  let off = getenv("LUDIC_CHECK")
+  if off != null and (off == "0") { return }
+  ck_index()
+  var i = 0
+  while i < g_prog_user_end {
+    let d = prog[i]
+    if d.kind == N_FN { ck_fn_body(d) }
+    if d.kind == N_MAIN or d.kind == N_TEST { ck_block(d.a) }
+    if (d.kind == N_VAR or d.kind == N_CONST) and d.a != null { ck_give(d.ty, ck_expr(d.a), d.a, d.s) }
+    i += 1
+  }
+  var j = 0
+  while j < len(g_onlisten) {
+    ck_listener(g_onlisten[j])
+    j += 1
+  }
+  if ck_errors > 0 and not ck_reporting() {
+    let m = `{itoa(ck_errors)} type error(s)\n`
+    file_write(file_stderr(), m, len(m))
+    exit(1)
+  }
+}

selfhost/check/check_types.ludic

@@ -0,0 +1,84 @@
+# check_types.ludic — L4: what a type is, and what may be given where. A type is its written
+# form ("int", "[]Thing", "fn(int)->bool"); "?" is a type the checker could not work out, and it
+# agrees with everything, so the checker only ever reports a mix-up it can prove. "null" is the
+# type of the null literal, and `pointer` is untyped: numbers, bools, text, records, slices and
+# functions are kept apart, and a pointer is trusted to be whatever it is given as.
+function ck_unknown(t: pointer) -> bool { return t == null or (t == "?") }
+function ck_is_int(t: pointer) -> bool {
+  if (t == "int") or (t == "long") or (t == "byte") or (t == "i64") or (t == "u8") { return true }
+  let en = ck_enum(t)
+  if en != null { return not enum_is_tagged(en) }
+  return false
+}
+# "an int", "a float": the article a message puts before a type
+function ck_a(t: pointer) -> pointer {
+  let c = t[0]
+  if c == 'a' or c == 'e' or c == 'i' or c == 'o' or c == 'u' or c == 'A' or c == 'E' or c == 'I' or c == 'O' or c == 'U' { return `an {t}` }
+  return `a {t}`
+}
+function ck_is_float(t: pointer) -> bool { return (t == "float") or (t == "double") }
+function ck_is_num(t: pointer) -> bool { return ck_is_int(t) or ck_is_float(t) or (t == "fixed") }
+function ck_is_rec(t: pointer) -> bool { return ck_record(t) != null }
+# a value that is an address: a string, a record, a slice, a buffer, a function, a boxed enum
+function ck_is_ref(t: pointer) -> bool {
+  if ck_is_num(t) or (t == "bool") or (t == "void") or (t == "null") { return false }
+  return true
+}
+# a literal takes the kind of the slot it is written into: `1` is a float in a float slot and
+# `1.5` a fixed in a fixed one, and `-1` is as much a literal as `1`
+function ck_is_lit(e: Node) -> bool {
+  if e == null { return false }
+  if e.kind == E_INT or e.kind == E_FLOAT { return true }
+  if e.kind == E_UN and (e.s == "-") { return ck_is_lit(e.a) }
+  return false
+}
+# the class a type belongs to, for an operator: n(umber) s(tring) b(ool) r(eference)
+function ck_class(t: pointer) -> pointer {
+  if ck_is_num(t) { return "number" }
+  if (t == "string") { return "string" }
+  if (t == "bool") { return "bool" }
+  return "reference"
+}
+
+# may a value of type `from` (the expression `e`) be given where `to` is wanted? null when it
+# may; otherwise the category of the mix-up, which is also how the report groups them
+function ck_mismatch(to: pointer, from: pointer, e: Node) -> pointer {
+  if ck_unknown(to) or ck_unknown(from) { return null }
+  if (to == from) or (to == "void") { return null }
+  if (from == "null") {
+    if ck_is_ref(to) { return null }
+    return "null"
+  }
+  if (to == "bool") or (from == "bool") { return "bool" }
+  # a decimal literal is whichever of float and fixed its slot is
+  if ck_is_lit(e) and ((from == "fixed") or ck_is_float(from)) and ((to == "fixed") or ck_is_float(to)) { return null }
+  if ck_is_int(to) {
+    if ck_is_int(from) { return null }
+    if ck_is_num(from) { return "narrowing" }
+    return "kind"
+  }
+  if ck_is_float(to) {
+    if ck_is_int(from) or ck_is_float(from) { return null }
+    if (from == "fixed") { return "fixed" }
+    return "kind"
+  }
+  if (to == "fixed") {
+    if ck_is_int(from) { return null }
+    if ck_is_float(from) and ck_is_lit(e) { return null }
+    if ck_is_float(from) { return "fixed" }
+    return "kind"
+  }
+  if ck_is_num(from) { return "kind" }
+  # `pointer` is the untyped reference, C's void *: it goes anywhere a reference does, and a
+  # reference goes into it. What it may hold is L7's question (unsafe), not this pass's.
+  if (to == "pointer") or (from == "pointer") { return null }
+  if (to == "string") { return "kind" }
+  if ck_is_rec(to) and ck_is_rec(from) { return "record" }
+  if ck_is_rec(to) and ((from == "string") or is_slice_ty(from)) { return "kind" }
+  # a []string is a []pointer that holds only text, and a []pointer is untyped
+  if (to == "[]pointer") or (from == "[]pointer") { return null }
+  if is_slice_ty(to) and is_slice_ty(from) { return "slice" }
+  if is_fn_type(to) and is_fn_type(from) { return "fn" }
+  if (from == "string") and (ck_is_rec(to) or is_slice_ty(to) or is_fn_type(to)) { return "kind" }
+  return null
+}

selfhost/frontend/parse.ludic

@@ -105,7 +105,7 @@ function ptype() -> pointer {
       if is_op(",") { pi += 1 }
     }
     eat_op(")")
-    var r = "void"
+    var r: pointer = "void"
     if is_op("->") {
       pi += 1
       r = ptype()

selfhost/main.ludic

@@ -202,6 +202,7 @@ entry {
   else { g_windowed = has_target and has_systems() }
 
   g_parsing = false                               # lowering errors now locate by statement, not token
+  check_program()                                 # L4: the types agree before anything is emitted
   emit_program()
 
   # --emit-llvm, or no binary target: emit IR and stop (stdout when out is null).

selfhost/support/io.ludic

@@ -1,7 +1,7 @@
 # io.ludic — reading the input file and writing the output, plus tiny stdio.
 # The compiler reads one .ludic file whole and emits LLVM IR text to stdout.
 
-function read_file(path: string) -> pointer {
+function read_file(path: pointer) -> pointer {
   let f = file_open(path, "rb")
   if (f == null) { return null }
   file_seek(f, 0, 2)

tools/ludic-cli/build.ludic

@@ -133,7 +133,7 @@ function threads_link_flags(ll: pointer) -> pointer {
 }
 
 # the file part of a path: everything after the last '/'
-function file_of_path(p: pointer) -> pointer {
+function file_of_path(p: pointer) -> string {
   let d = dir_of_path(p)
   if len(d) == 0 { return p }
   return p[len(d) + 1..len(p)]

tools/ludic-cli/docgen.ludic

@@ -44,7 +44,7 @@ function sb_putc(s: Sb, c: int) -> void {
   s.data[s.len] = c
   s.len += 1
 }
-function sb_str(s: Sb) -> pointer {
+function sb_str(s: Sb) -> string {
   s.data[s.len] = 0
   return s.data
 }
@@ -134,7 +134,7 @@ function strs_sort(a: []pointer) -> void {
 
 # `<code>` backtick spans: `x` -> <code>x</code> (inner text NOT escaped).
 # Mirrors codeify's re.sub(r"`([^`]+)`", ...): needs >=1 non-backtick inside.
-function codeify(s: pointer) -> pointer {
+function codeify(s: pointer) -> string {
   let n = slen(s)
   let b = sb_new()
   var i = 0

tools/ludic-cli/glgen.ludic

@@ -405,7 +405,9 @@ function glg_emit_ludic(path: pointer) -> bool {
       sb_puts(ps, `{glg_pname(glg_ppname[ix], p)}: {lt}`)
       p += 1
     }
-    let rt = glg_ludic_ty(glg_frbase[i], glg_frstar[i])
+    var rt = glg_ludic_ty(glg_frbase[i], glg_frstar[i])
+    # a returned `const GLubyte *` is the driver's text (glGetString): a string, not memory
+    if glg_frstar[i] == 1 and (glg_frbase[i] == "GLubyte" or glg_frbase[i] == "GLchar") { rt = "string" }
     var rets = ""
     if rt != "void" { rets = " -> " + rt }
     sb_puts(b, `extern function {lname}({sb_str(ps)}){rets} = "lgl_{glg_fname[i]}"\n`)

tools/ludic-cli/json.ludic

@@ -51,7 +51,7 @@ function utf8_put(b: pointer, n: int, cp: int) -> int {
 }
 
 # parse a JSON string starting at the opening quote; returns a fresh buffer
-function j_string() -> pointer {
+function j_string() -> string {
   jpos += 1                                   # opening quote
   # over-allocate: escapes only ever shrink the byte count
   let cap = slen(jbuf) - jpos + 1

tools/ludic-cli/pack.ludic

@@ -437,7 +437,7 @@ function pack_roots(m: Manifest, from: int) -> []pointer {
 }
 
 # the pack a project builds by default: build/<name>.lpak
-function pack_default_out(m: Manifest) -> pointer {
+function pack_default_out(m: Manifest) -> string {
   return `build/{project_name("")}.lpak`
 }
 

tools/ludic-cli/prelude.ludic

@@ -13,7 +13,7 @@
 # ---- file IO ----------------------------------------------------------------
 
 # read a whole file into a fresh NUL-terminated buffer (null if it cannot open)
-function read_file(path: pointer) -> pointer {
+function read_file(path: pointer) -> string {
   let f = file_open(path, "rb")
   if (f == null) { return null }
   file_seek(f, 0, 2)
@@ -122,7 +122,7 @@ function tmp_dir() -> pointer {
 }
 
 # a scratch path under tmp_dir(): tmp_path("foo.out")
-function tmp_path(name: pointer) -> pointer { return `{tmp_dir()}/{name}` }
+function tmp_path(name: pointer) -> string { return `{tmp_dir()}/{name}` }
 
 # remove the scratch directory (idempotent; a no-op when nothing was written).
 # LUDIC_KEEP_TMP=1 leaves it in place, and says where, for debugging a failing case.
@@ -147,7 +147,7 @@ function capture(cmd: pointer) -> pointer {
 
 # run `cmd`, join its output lines with single spaces and trim — the Ludic twin
 # of the shell idiom `$(cmd | tr '\n' ' ' | sed 's/ *$//')`.
-function capture_line(cmd: pointer) -> pointer {
+function capture_line(cmd: pointer) -> string {
   return capture(`{cmd} | tr '\n' ' ' | sed 's/ *$//'`)
 }
 
@@ -233,7 +233,7 @@ function report() -> int {
 }
 
 # a positional argument, or a default when it is absent
-function argn(i: int, dflt: pointer) -> pointer {
+function argn(i: int, dflt: pointer) -> string {
   if (i < arg_count()) { return arg(i) }
   return dflt
 }
@@ -399,7 +399,7 @@ function line_at(s: pointer, start: int) -> pointer {
 }
 
 # trim leading/trailing ASCII whitespace (space, tab, cr, nl)
-function s_trim(s: pointer) -> pointer {
+function s_trim(s: pointer) -> string {
   let n = slen(s)
   var a = 0
   while a < n and (is_ws(s[a]) or s[a] == '\n' or s[a] == '\r') { a += 1 }

tools/ludic-cli/release.ludic

@@ -31,7 +31,7 @@ function has_changesets() -> bool {
 # the highest bump level requested across the pending changesets ("" if none).
 # README.md is excluded — its format example carries a literal `bump:` line that
 # must not count as a real changeset.
-function highest_bump() -> pointer {
+function highest_bump() -> string {
   if shq("grep -rhqE '^bump:[[:space:]]*major' --include='*.md' --exclude='README.md' changes 2>/dev/null") { return "major" }
   if shq("grep -rhqE '^bump:[[:space:]]*minor' --include='*.md' --exclude='README.md' changes 2>/dev/null") { return "minor" }
   if shq("grep -rhqE '^bump:[[:space:]]*patch' --include='*.md' --exclude='README.md' changes 2>/dev/null") { return "patch" }

tools/ludic-cli/selfhost.ludic

@@ -55,6 +55,13 @@ function selfhost_frags() -> []pointer {
   push(f, "selfhost/backend/emit_call.ludic")
   push(f, "selfhost/backend/emit_fnval.ludic")
   push(f, "selfhost/backend/emit_vis.ludic")
+  push(f, "selfhost/check/check_index.ludic")
+  push(f, "selfhost/check/check_types.ludic")
+  push(f, "selfhost/check/check_env.ludic")
+  push(f, "selfhost/check/check_expr.ludic")
+  push(f, "selfhost/check/check_ops.ludic")
+  push(f, "selfhost/check/check_call.ludic")
+  push(f, "selfhost/check/check_stmt.ludic")
   push(f, "selfhost/backend/emit_stmt.ludic")
   push(f, "selfhost/backend/game/emit_ecs.ludic")
   push(f, "selfhost/backend/game/emit_query.ludic")

tools/ludic-cli/shaders.ludic

@@ -161,7 +161,7 @@ function shd_file(name: pointer) -> pointer {
 
 function shd_q(p: pointer) -> pointer { return `"{p}"` }
 
-function shd_reflect_stage(mf: pointer, id: pointer, stage: pointer, spv: pointer, tmp: pointer) -> bool {
+function shd_reflect_stage(mf: Sb, id: pointer, stage: pointer, spv: pointer, tmp: pointer) -> bool {
   let js = `{tmp}/{id}.{stage}.json`
   if not shq(`{shd_q(shd_bin + "/spirv-cross")} {shd_q(spv)} --reflect > {shd_q(js)} 2>/dev/null`) { err(`shaders: spirv-cross failed on {spv}\n`);  return false }
   let d = json_parse(read_file(js))

tools/ludic-cli/test.ludic

@@ -31,6 +31,17 @@ function reject_case(path: pointer, want: pointer, label: pointer) -> void {
   if s_contains(got, want) { ok(label) } else { bad2(label, `refused, but said [{got}]`) }
 }
 
+# a program the checker refuses for exactly `n` reasons, all of them reported in one run
+function reject_count(path: pointer, n: int, label: pointer) -> void {
+  let ll = `{tmp_dir()}/rj_{flat(path)}.ll`
+  if shq(`bin/ludicc examples/{path}.ludic --emit-llvm -o {ll} 2>{tmp_dir()}/rj.err`) {
+    bad2(label, "compiled, and should have been refused")
+    return
+  }
+  let got = capture_line(`grep -c ': error:' {tmp_dir()}/rj.err`)
+  if (got == string(n)) { ok(label) } else { bad2(label, `reported {got} error(s), not {n}`) }
+}
+
 # a feature example that consumes an in-repo controller package (packages/): same
 # as feat_case, but the compiler is pointed at packages/ via LUDIC_MODULES so a
 # `import "ludic.foo/bar.ludic"` resolves, and LUDIC_HOME anchors the engine
@@ -705,9 +716,16 @@ function cmd_dev_test() -> int {
   reject_case("rejected/redeclared_local", "'v0' is declared twice in this block", "a local declared twice in one block is refused")
   reject_case("rejected/missing_return", "can reach its end without returning", "a function that can run off its end without its result is refused")
   feat_case("functions/values", "", "42 10 25 49 81 1.5 1", "values.ludic (L2: fn types, fn name, calls through a local, global, field, element, parameter, result)")
-  reject_case("rejected/fn_type_mismatch", "is not a fn(int)->int", "a function of the wrong type is refused")
+  reject_case("rejected/fn_type_mismatch", "op wants a fn(int)->int and this is a fn(float)->float", "a function of the wrong type is refused")
   feat_case("modules/visible", "", "42 42", "visible.ludic (L3: a module's exported function and event used from outside it)")
   reject_case("rejected/private_module", "add is private to module bank", "a private function of another module is refused")
+  feat_case("lang/checked", "", "7.5 3 12 hi 2 ok", "checked.ludic (L4: literals take their slot's kind, string(p), []string as []pointer, null, named args)")
+  reject_case("rejected/wrong_arity", "area takes 2 argument(s) and this call gives 1", "a call with the wrong number of arguments is refused")
+  reject_case("rejected/float_into_int", "metres wants an int and this is a float", "a float computed into an int is refused")
+  reject_case("rejected/record_mixup", "d wants a Door and this is a Key", "one record type is not another")
+  reject_case("rejected/record_as_text", "argument 1 of sign wants a string and this is a Trail", "a record is not text")
+  reject_case("rejected/text_plus_number", "text joins text only", "text plus a number is refused")
+  reject_count("rejected/every_error", 3, "every type error in a program is reported at once, not only the first")
 
   # EV2 the world table: the mod reflection ABI, callable from Ludic by name.
   net_case("ecs/world_get", "50 1 7")