Add built-in string operations for searching and transforming strings. Currently Vera has 13 string builtins (length, concat, slice, char_code, strip, parse_nat, parse_float64, to_string, and the v0.0.64 type-to-string family), but lacks common search and transformation operations.

Proposed functions

Search

• string_contains(@String, @String -> @Bool) — substring search
• starts_with(@String, @String -> @Bool) — prefix check
• ends_with(@String, @String -> @Bool) — suffix check
• index_of(@String, @String -> @Option<Nat>) — first occurrence index (None if not found)

Transformation

• to_upper(@String -> @String) — ASCII uppercase
• to_lower(@String -> @String) — ASCII lowercase
• replace(@String, @String, @String -> @String) — replace all occurrences
• split(@String, @String -> @Array<String>) — split by delimiter
• join(@Array<String>, @String -> @String) — join with separator

Implementation notes

All are pure functions. Search operations are simple byte-level loops in WAT. Transformation operations allocate via the bump allocator. split returns an Array<String> (compound array support landed in v0.0.61). join is the inverse.

The pattern for adding builtins is established: register in environment.py, implement in wasm/calls.py, add inference in wasm/inference.py, add to known set in codegen/modules.py.

Dependencies

• None (all infrastructure exists)
• split benefits from compound array codegen (Arrays of compound types in codegen #132, done)