String/atom predicates: var/nonvar/atom/number/compound/callable/atomic/is_list + atom_length/atom_concat/atom_chars/atom_codes/char_code/number_codes/number_chars

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

plans/prolog-on-sx.md

@@ -69,7 +69,7 @@ Representation choices (finalise in phase 1, document here):
 - [x] `assert/1`, `asserta/1`, `assertz/1`, `retract/1` — `assert` aliases `assertz`. Helpers `pl-rt-to-ast` (deep-walk + replace runtime vars with `_G<id>` parse markers) + `pl-build-clause` (detect `:-` head). `assertz` uses `pl-db-add!`; `asserta` uses new `pl-db-prepend!`. `retract` walks goal, looks up by functor/arity, tries each clause via unification, removes first match by index (`pl-list-without`). 11 tests in `tests/dynamic.sx`. Rule-asserts deferred — `:-` not in op table yet, so only fact-shaped clauses for now.
 - [x] `findall/3`, `bagof/3`, `setof/3` — shared `pl-collect-solutions` runs the goal in a fresh cut-box, deep-copies the template (via `pl-deep-copy` with var-map for shared-var preservation) on each success, returns false to backtrack, then restores trail. `findall` always succeeds with a (possibly empty) list. `bagof` fails on empty. `setof` builds a string-keyed dict via `pl-format-term` for sort+dedupe (via `keys` + `sort`), fails on empty. Existential `^` deferred (operator). 11 tests in `tests/findall.sx`.
 - [x] `copy_term/2`, `functor/3`, `arg/3`, `=../2` — `copy_term/2` reuses `pl-deep-copy` with a fresh var-map (preserves source aliasing). `functor/3` handles 4 modes: compound→{name, arity}, atom→{atom, 0}, num→{num, 0}, var with ground name+arity→constructed term (`pl-make-fresh-args` for compound case). `arg/3` extracts 1-indexed arg from compound. **`=../2` deferred** — the tokenizer treats `.` as the clause terminator unconditionally, so `=..` lexes as `=` + `.` + `.`; needs special-case lex (or surface syntax via a different name). 14 tests in `tests/term_inspect.sx`.
-- [ ] String/atom predicates
+- [x] String/atom predicates
 
 ### Phase 5 — Hyperscript integration
 - [ ] `prolog-query` primitive callable from SX/Hyperscript
@@ -88,6 +88,7 @@ Representation choices (finalise in phase 1, document here):
 
 _Newest first. Agent appends on every commit._
 
+- 2026-04-25 — String/atom predicates. Type-test predicates: `var/1`, `nonvar/1`, `atom/1`, `number/1`, `integer/1`, `float/1` (always-fail), `compound/1`, `callable/1`, `atomic/1`, `is_list/1`. String/atom operations: `atom_length/2`, `atom_concat/3` (3 modes: both-ground, result+first, result+second), `atom_chars/2` (bidirectional), `atom_codes/2` (bidirectional), `char_code/2` (bidirectional), `number_codes/2`, `number_chars/2`. 7 helper functions in runtime.sx (`pl-list-to-prolog`, `pl-proper-list?`, `pl-prolog-list-to-sx`, `pl-solve-atom-concat!`, `pl-solve-atom-chars!`, `pl-solve-atom-codes!`, `pl-solve-char-code!`). 34 tests in `tests/atoms.sx`. Total **272** (+34).
 - 2026-04-25 — `copy_term/2` + `functor/3` + `arg/3` (term inspection). `copy_term` is a one-line dispatch to existing `pl-deep-copy`. `functor/3` is bidirectional — decomposes a bound compound/atom/num into name+arity OR constructs from ground name+arity (atom+positive-arity → compound with N anonymous fresh args via `pl-make-fresh-args`; arity 0 → atom/num). `arg/3` extracts 1-indexed arg with bounds-fail. New helper `pl-solve-eq2!` for paired-unification with shared trail-undo. 14 tests in `tests/term_inspect.sx`. Total **238** (+14). `=..` deferred — `.` always tokenizes as clause terminator; needs special lexer case.
 - 2026-04-25 — `findall/3` + `bagof/3` + `setof/3`. Shared collector `pl-collect-solutions` runs the goal in a fresh cut-box, deep-copies the template per success (`pl-deep-copy` walks term, allocates fresh runtime vars via shared var-map so co-occurrences keep aliasing), returns false to keep backtracking, then `pl-trail-undo-to!` to clean up. `findall` always builds a list. `bagof` fails on empty. `setof` uses a `pl-format-term`-keyed dict + SX `sort` for dedupe + ordering. New `tests/findall.sx` 11 tests. Total **224** (+11). Existential `^` deferred — needs operator.
 - 2026-04-25 — Dynamic clauses: `assert/1`, `assertz/1`, `asserta/1`, `retract/1`. New helpers `pl-rt-to-ast` (deep-walk runtime term → parse-AST, mapping unbound runtime vars to `_G<id>` markers so `pl-instantiate-fresh` produces fresh vars per call) + `pl-build-clause` + `pl-db-prepend!` + `pl-list-without`. `retract` keeps runtime vars (so the caller's vars get bound), walks head for the functor/arity key, tries each stored clause via `pl-unify!`, removes the first match by index. 11 tests in `tests/dynamic.sx`; conformance script gained dynamic row. Total **213** (+11). Rule-form asserts (`(H :- B)`) deferred until `:-` is in the op table.