Progress log: io_predicates batch, 456/456

plans/prolog-on-sx.md

@@ -88,6 +88,7 @@ Representation choices (finalise in phase 1, document here):
 
 _Newest first. Agent appends on every commit._
 
+- 2026-04-25 — IO/term predicates: `term_to_atom/2` (bidirectional: format term or parse atom), `term_string/2` (alias), `with_output_to/2` (atom/string sinks — saves/restores `pl-output-buffer`), `writeln/1`, `format/1` (~n/~t/~~), `format/2` (~w/~a/~d pull from arg list). 24 tests in `tests/io_predicates.sx`. Total **456** (+24).
 - 2026-04-25 — Char predicates: `char_type/2` (9 modes: alpha/alnum/digit/digit(N)/space/white/upper(L)/lower(U)/ascii(C)/punct), `upcase_atom/2`, `downcase_atom/2`, `string_upper/2`, `string_lower/2`. 10 helpers using `char-code`/`char-from-code` SX primitives. 27 tests in `tests/char_predicates.sx`. Total **432** (+27).
 - 2026-04-25 — Set/fold predicates: `foldl/4` (CPS fold-left, threads accumulator via `pl-apply-goal`), `list_to_set/2` (dedup preserving first-occurrence), `intersection/3`, `subtract/3`, `union/3` (all via `pl-struct-eq?`). 3 new helpers, 15 tests in `tests/set_predicates.sx`. Total **405** (+15).
 - 2026-04-25 — Meta-call predicates: `forall/2` (negation-of-counterexample), `maplist/2` (goal over list), `maplist/3` (map goal building output list), `include/3` (filter by goal success), `exclude/3` (filter by goal failure). New `pl-apply-goal` helper extends a goal with extra args. 15 tests in `tests/meta_call.sx`. Total **390** (+15).