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Phase 7h: string slicing s[a..b] (retire substr)

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`s[a..b]` is a fresh substring of the bytes [a, b) — the modern, end-based form
of the C-style `substr(s, start, count)`:

  substr(src, start, i - start)   -> src[start..i]
  substr(t, 2, len(t) - 2)        -> t[2..len(t)]
  substr(src, i, 2)               -> src[i..i + 2]

Mechanics: a new E_SLICE postfix (`base[lo..hi]`, distinct from `base[i]`
indexing) lowers to a @fn_str_slice prelude (malloc + copy + terminate), emitted
once into any program that slices. Two reseeds: add the syntax + prelude, then
migrate the 22 substr calls and delete substr. The migrator recognises the
common `count == end - start` shape and emits the clean `s[start..end]` rather
than `s[start..start + (end - start)]`.

examples/strings.ludic gains slicing (now prints 1..9). Reseeded (22673 lines);
C-free fixpoint holds; goldens identical; 18/18; vocab + doc-fences clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
Orkun ÇAKILKAYA 2026-08-28 01:35:24 +03:00
parent 0efa06dca2
commit 1b9789630a
14 changed files with 4049 additions and 3914 deletions
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7
selfhost/emit_expr.ludic
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@ -178,6 +178,13 @@ fn emit_expr(e: Node) -> Val {
if e.kind == E_FLOAT { return val(itoa(e.ival), "fixed") }
if e.kind == E_BOOL { return val(itoa(e.ival), "bool") }
if e.kind == E_NULL { return val("null", "ptr") }
if e.kind == E_SLICE { # s[a..b] -> a fresh substring
let base = emit_expr(e.a)
let lo = emit_expr(e.b)
let hi = emit_expr(e.c)
g_uses_strslice = true
return val(emit_bind(`call ptr @fn_str_slice(ptr {base.code}, i32 {lo.code}, i32 {hi.code})`), "str")
}
if e.kind == E_STR { return val(emit_str_const(e.s), "str") }
if e.kind == E_NEW {
if is_slice_ty(e.s) { return emit_new_slice(e.s) }