# check_gen_call.ludic — L5: a call to a generic function. Its arguments' types bind the type
# parameters (a literal only binds what nothing else did, so first(xs, 0) is decided by xs), the
# slot the call is written into binds what they cannot, and the call is rewritten to name the
# instance: `first(xs)` on a []int calls first$int, which is made and checked once however many
# calls reach it.
function gen_instance_name(name: pointer, binds: []pointer) -> pointer {
  var out: pointer = name
  var i = 0
  while i < len(binds) {
    out = out + "$" + gen_mangle(binds[i])
    i += 1
  }
  return out
}
function gen_fn_instance(t: Node, iname: pointer, binds: []pointer) -> Node {
  let have = ck_fn(iname)
  if have != null { return have }
  let f = gen_clone(t, gen_split(t.tps), binds)
  f.s = iname
  if g_migrate { f.mg = mg_unit(t, 0) }        # an instance's needs are its generic's
  push(g_gen_out, f)
  push(g_gen_work, f)
  ck_tab_put(ck_fn_k, ck_fn_v, iname, f)
  return f
}
# each parameter's argument node, positional or named
function gen_arg_nodes(e: Node, labels: []pointer) -> []Node {
  let out = new []Node
  var i = 0
  while i < len(labels) {
    push(out, null)
    i += 1
  }
  var j = 0
  while j < len(e.kids) {
    let k = e.kids[j]
    if k.kind == E_FINIT {
      let at = gen_index(labels, k.s)
      if at >= 0 { out[at] = k.a }
    } else {
      if j < len(out) { out[j] = k }
    }
    j += 1
  }
  return out
}
function gen_call(e: Node, name: pointer, t: Node) -> pointer {
  mg_call(e, t)
  let expect = ck_call_expect
  call_fill_defaults(e, t)
  let tps = gen_split(t.tps)
  let labels = new []pointer
  let ptys = new []pointer
  ck_params(t, labels, ptys)
  if len(e.kids) != len(ptys) { ck_err("arity", e, `{name} takes {itoa(len(ptys))} argument(s) and this call gives {itoa(len(e.kids))}`) }
  let nodes = gen_arg_nodes(e, labels)
  let atys = new []pointer
  let binds = new []pointer
  var i = 0
  while i < len(tps) {
    push(binds, null)
    i += 1
  }
  i = 0
  while i < len(nodes) {
    var at: pointer = "?"
    if nodes[i] != null { at = ck_expr(nodes[i]) }
    push(atys, at)
    if nodes[i] != null and not ck_is_lit(nodes[i]) { gen_unify(ptys[i], at, tps, binds) }
    i += 1
  }
  gen_unify(t.ty, expect, tps, binds)
  i = 0
  while i < len(nodes) {
    if nodes[i] != null and ck_is_lit(nodes[i]) { gen_unify(ptys[i], atys[i], tps, binds) }
    i += 1
  }
  var k = 0
  while k < len(tps) {
    if binds[k] == null {
      ck_err("generic", e, `cannot tell what {tps[k]} is in this call to {name}: pass it an argument that says, or write the call where its result has a declared type`)
      return "?"
    }
    k += 1
  }
  let f = gen_fn_instance(t, gen_instance_name(name, binds), binds)
  e.a.s = f.s
  let fl = new []pointer
  let fp = new []pointer
  ck_params(f, fl, fp)
  var j = 0
  while j < len(nodes) {
    if nodes[j] != null { ck_give(fp[j], atys[j], nodes[j], `argument {itoa(j + 1)} of {name}`) }
    j += 1
  }
  return f.ty
}
# every instance a generic body asks for is made and checked in turn; then the records the
# program only ever names in a type, and the instances go back in where the program's own
# declarations end
function gen_finish() -> void {
  var w = 0
  while w < len(g_gen_work) {
    ck_fn_body(g_gen_work[w])
    w += 1
  }
  var r = 0
  while r < len(g_gi_name) {
    if g_gi_open[r] == 0 and gen_template(g_gen_recs, g_gi_gen[r]) != null { ck_record(g_gi_name[r]) }
    r += 1
  }
  if len(g_gen_out) == 0 { return }
  let np = new []Node
  var i = 0
  while i < len(prog) {
    if i == g_prog_user_end {
      var o = 0
      while o < len(g_gen_out) {
        push(np, g_gen_out[o])
        o += 1
      }
    }
    push(np, prog[i])
    i += 1
  }
  if g_prog_user_end >= len(prog) {
    var o2 = 0
    while o2 < len(g_gen_out) {
      push(np, g_gen_out[o2])
      o2 += 1
    }
  }
  prog = np
  g_prog_user_end += len(g_gen_out)
}