`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>
Orkuncakilkaya
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