ludic/selfhost/frontend/state.ludic

# state.ludic — 0.S: no function writes a global. A module's changing data is a `state` record:
#
#   state Hiker { hips: int = -1, spine: int = -1 }
#
# The program holds exactly one instance of each, which no code can name - it is the hidden global
# `state$Hiker` (a name the lexer cannot produce). It reaches code only as a parameter, `h: mut
# Hiker` to change it or `h: Hiker` to read it, and the runtime supplies it at the entry points:
#   - a body that declares it: `entry (h: mut Hiker)`, `handler Draw(h: Hiker) phase Render`,
#     `@On(E) handler Heard(h: mut Hiker)`, `test "name" (h: mut Hiker)` - each is a `let` at the
#     body's top bound to the instance;
#   - a function value: `fn f` of a function whose leading parameters are states is that function
#     with them supplied (emit_fnval.ludic writes the thunk), so a system, a port's bind and any
#     callback a package calls are entry points without saying so;
#   - a call the compiler writes: a namespace method's target, a runtime built-in.
# A module-level `var` is refused (a `state` holds it), unless the build says --globals (the
# toolchain's own programs, which are not part of this); a module-level `let` is deeply immutable.
var g_state_names: []pointer = new []pointer
var g_allow_globals: bool = false
var g_gen_nodes: bool = false          # the finishing passes are writing code: its nodes are generated

# a runtime function called from outside the runtime: a built-in, whose states are the runtime's
function is_runtime_file(f: pointer) -> bool { return f != null and has_sub(f, "runtime/native/") }
function state_inject_runtime(e: Node, f: Node) -> void {
  if e != null and f != null and is_runtime_file(f.file) and not is_runtime_file(e.file) { state_inject(e, f) }
}
# a call the compiler wrote itself (a view's model, a component's glue): its callee's states are
# supplied - the runtime's side of an entry point
function state_inject_generated(e: Node, f: Node) -> void {
  if e != null and e.pos < 0 { state_inject(e, f) }
}
# `(h: mut Hiker)` copied onto the front of a function's parameters (a view's functions)
function state_params_onto(f: Node, ps: []Node) -> void {
  if len(ps) == 0 { return }
  let kids = new []Node
  var i = 0
  while i < len(ps) {
    let p = node(N_PARAM)
    p.s = ps[i].s
    p.ty = ps[i].ty
    p.uns = ps[i].uns
    p.file = ps[i].file
    p.line = ps[i].line
    push(kids, p)
    i += 1
  }
  i = 0
  while i < len(f.kids) {
    push(kids, f.kids[i])
    i += 1
  }
  f.kids = kids
}

function state_global(name: pointer) -> pointer { return `state${name}` }
function is_state_ty(t: pointer) -> bool {
  if t == null { return false }
  var i = 0
  while i < len(g_state_names) {
    if (g_state_names[i] == t) { return true }
    i += 1
  }
  return false
}
# state NAME { fields } - a record, and its one instance
function parse_state() -> void {
  let c = parse_component()
  c.uns = 2
  push(prog, c)
  push(g_state_names, c.s)
  let v = node(N_VAR)
  v.s = state_global(c.s)
  v.ty = c.s
  v.line = c.line
  v.uns = 1
  let nw = node(E_NEW)
  nw.s = c.s
  nw.file = c.file
  nw.line = c.line
  v.a = nw
  push(prog, v)
}
# `name: mut T` in a parameter list: the `mut`, when it is there
function parse_param_mut(p: Node) -> void {
  p.pos2 = toks[pi].pos                        # where `mut ` goes, when a migration adds it
  if is_id("mut") and toks[pi + 1].kind == TK_ID {
    pi += 1
    p.uns = 1
  }
}
# `(h: mut Hiker, ...)` before an entry point's body: the states the runtime supplies, as the
# `let`s that open the body
function parse_entry_params() -> []Node {
  let out = new []Node
  if not is_op("(") { return out }
  pi += 1
  while not is_op(")") {
    skipnl()
    let p = node(N_PARAM)
    p.s = eat_id()
    eat_op(":")
    parse_param_mut(p)
    p.ty = ptype()
    push(out, p)
    skipnl()
    if is_op(",") { pi += 1 }
  }
  eat_op(")")
  return out
}
# a call the compiler writes (a namespace method's target, a runtime built-in) to a function whose
# leading parameters are states: the instances, unless the call already gives every parameter
function state_inject(e: Node, f: Node) -> void {
  if f == null or e == null { return }
  var k = 0
  var total = 0
  var i = 0
  while i < len(f.kids) {
    if f.kids[i].kind == N_PARAM {
      if total == k and is_state_ty(f.kids[i].ty) { k += 1 }
      total += 1
    }
    i += 1
  }
  if k == 0 or len(e.kids) + k > total { return }
  var named = false                              # `f(x: 1)`: the states go in by name too
  i = 0
  while i < len(e.kids) {
    if e.kids[i].kind == E_FINIT { named = true }
    i += 1
  }
  let args = new []Node
  i = 0
  while i < k {
    let id = node(E_ID)
    id.s = state_global(f.kids[i].ty)
    id.file = e.file
    id.line = e.line
    if named {
      let fi = node(E_FINIT)
      fi.s = f.kids[i].s
      fi.a = id
      push(args, fi)
    } else { push(args, id) }
    i += 1
  }
  i = 0
  while i < len(e.kids) {
    push(args, e.kids[i])
    i += 1
  }
  e.kids = args
}
# a retained `ui` block is an entry point: `font: MenuState.title_font` reads the instance
function ui_state_refs(n: Node) -> void {
  if n == null { return }
  if n.kind == E_MEMBER and n.a != null and n.a.kind == E_ID and is_state_ty(n.a.s) { n.a.s = state_global(n.a.s) }
  ui_state_refs(n.a)
  ui_state_refs(n.b)
  ui_state_refs(n.c)
  var i = 0
  while i < len(n.kids) {
    ui_state_refs(n.kids[i])
    i += 1
  }
}
function ui_blocks_states() -> void {
  var i = 0
  while i < len(prog) {
    if prog[i].kind == N_UI and prog[i].ival == 1 { ui_state_refs(prog[i].a) }
    i += 1
  }
}
function entry_bind(body: Node, ps: []Node) -> void {
  if len(ps) == 0 or body == null { return }
  let lets = new []Node
  var i = 0
  while i < len(ps) {
    let p = ps[i]
    let l = node(S_LET)
    l.s = p.s
    l.ty = p.ty
    l.file = p.file
    l.line = p.line
    l.ival = 0
    l.uns = p.uns                                # 1: a `mut` state; 0: read-only
    l.tps = "state"                              # an entry point's state: checked to be one
    l.pos2 = p.pos2
    l.pos = p.pos
    let id = node(E_ID)
    id.s = state_global(p.ty)
    id.file = p.file
    id.line = p.line
    l.a = id
    push(lets, l)
    i += 1
  }
  var k = 0
  while k < len(body.kids) {
    push(lets, body.kids[k])
    k += 1
  }
  body.kids = lets
}