ludic/selfhost/check/check_expr.ludic

# 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 or n.kind == S_UNSAFE { ck_stmt(n);  return }
  ck_expr(n)
}
function ck_expr(e: Node) -> pointer {
  if e == null { return "?" }
  let ex = ck_expect
  ck_expect = null
  let k = e.kind
  if k == E_INT {
    if e.s != null { return "long" }              # a literal past 2^31 - 1
    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)
    ck_vis(f, e.s, e)
    if f != null { return fn_sig_of(f) }
    # the emitter's own refusal, here too, so a check-only build finds it (a bind to a function
    # that is gone)
    if find_fn(e.s) == null { ck_err("fnref", e, `fn {e.s}: no function called {e.s}`) }
    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 {
    ck_call_expect = ex
    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 {
    mg_local_use(e, ck_tys[li])                  # 0.S2 --migrate-prune: a state used here
    return ck_tys[li]
  }
  let g = ck_global(e.s)
  if g != null {
    mg_ref(e, g)
    ck_vis(g, e.s, e)
    return g.ty
  }
  let fv = mg_field_var(e.s)                     # 0.S2: a var a package moved into its state
  if fv != null {
    mg_ref(e, fv)
    return fv.ty
  }
  return "?"
}
# --check: the module rules (uses, export, ports - emit_vis.ludic) asked here, where every reference
# is resolved, since a check-only build stops before the emitter that asks them otherwise
var g_check_only: bool = false
var ck_vis_file: pointer = null   # a global's initializer is its declaration's file's code (as emitted)
var ck_vis_skip: bool = false     # a port's bind, checked where it was written (ports.ludic)
function ck_vis(d: Node, name: pointer, at: Node) -> void {
  if not g_check_only or ck_vis_skip or d == null or at == null or at.file == null { return }
  g_err_file = at.file
  if ck_vis_file != null { g_err_file = ck_vis_file }
  g_err_line = at.line
  vis_check(d, name)
}
function ck_new(e: Node) -> pointer {
  let r = ck_record(e.s)
  ck_vis(r, e.s, e)
  if r == null and g_check_only and port_find(e.s) >= 0 {
    ck_err("port", e, `{e.s} is a port: it is filled once with 'bind {e.s} {{ ... }}' where the program is put together, not made with new`)
  }
  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}`) }
        if ft == null { ck_err("field", fi.a, `{gen_show(e.s)} has no field {fi.s}`) }
      }
      i += 1
    }
  }
  return e.s
}
function ck_list(e: Node) -> pointer {
  var t: pointer = "?"
  var i = 0
  let saved = ck_vis_file
  while i < len(e.kids) {
    # a registry's entries are their defs' files' code (emit_list_elem)
    if saved != null and e.kids[i].file != null { ck_vis_file = e.kids[i].file }
    let et = ck_expr(e.kids[i])
    ck_vis_file = saved
    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 ck_is_raw(bt) { ck_raw(e, `indexing {ck_a(bt)}`) }
  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 "?"
}