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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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13
selfhost/emit_head.ludic
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@ -175,3 +175,16 @@ fn emit_int_str() -> void {
emith("fin:\n %fpos = phi i32 [ %pos, %sign ], [ %posn, %addneg ]\n")
emith(" %rpos = add i32 %fpos, 1\n %res = getelementptr inbounds i8, ptr %buf, i32 %rpos\n ret ptr %res\n}\n")
}
# s[a..b] -> a fresh NUL-terminated copy of the bytes [a, b), emitted (once) into
# any program that slices a string. Mallocs (b-a)+1, copies, terminates.
fn emit_str_slice() -> void {
emith("define ptr @fn_str_slice(ptr %s, i32 %start, i32 %end) {\n")
emith("entry:\n %len = sub i32 %end, %start\n %sz = add i32 %len, 1\n")
emith(" %sz64 = sext i32 %sz to i64\n %out = call ptr @malloc(i64 %sz64)\n br label %loop\n")
emith("loop:\n %i = phi i32 [ 0, %entry ], [ %i1, %body ]\n")
emith(" %d = icmp slt i32 %i, %len\n br i1 %d, label %body, label %fin\n")
emith("body:\n %si = add i32 %start, %i\n %sp = getelementptr inbounds i8, ptr %s, i32 %si\n %c = load i8, ptr %sp\n")
emith(" %op = getelementptr inbounds i8, ptr %out, i32 %i\n store i8 %c, ptr %op\n %i1 = add i32 %i, 1\n br label %loop\n")
emith("fin:\n %tp = getelementptr inbounds i8, ptr %out, i32 %len\n store i8 0, ptr %tp\n ret ptr %out\n}\n")
}