erlang: core BIFs + funs, Phase 2 complete (+35 tests)

plans/erlang-on-sx.md

@@ -60,8 +60,8 @@ Core mapping:
 - [x] `erlang-eval-ast`: evaluate sequential expressions — **54/54 tests**
 - [x] Pattern matching (atoms, numbers, vars, tuples, lists, `[H|T]`, underscore, bound-var re-match) — **21 new eval tests**; `case ... of ... end` wired
 - [x] Guards: `is_integer`, `is_atom`, `is_list`, `is_tuple`, comparisons, arithmetic — **20 new eval tests**; local-call dispatch wired
-- [ ] BIFs: `length/1`, `hd/1`, `tl/1`, `element/2`, `tuple_size/1`, `atom_to_list/1`, `list_to_atom/1`, `lists:map/2`, `lists:foldl/3`, `lists:reverse/1`, `io:format/1-2`
-- [ ] 30+ tests in `lib/erlang/tests/eval.sx`
+- [x] BIFs: `length/1`, `hd/1`, `tl/1`, `element/2`, `tuple_size/1`, `atom_to_list/1`, `list_to_atom/1`, `lists:map/2`, `lists:foldl/3`, `lists:reverse/1`, `io:format/1-2` — **35 new eval tests**; funs + closures wired
+- [x] 30+ tests in `lib/erlang/tests/eval.sx` — **130 tests green**
 
 ### Phase 3 — processes + mailboxes + receive (THE SHOWCASE)
 - [ ] Scheduler in `runtime.sx`: runnable queue, pid counter, per-process state record
@@ -99,6 +99,7 @@ Core mapping:
 
 _Newest first._
 
+- **2026-04-24 core BIFs + funs green** — Phase 2 complete. Added to `lib/erlang/transpile.sx`: fun values (`{:tag "fun" :clauses :env}`), fun evaluation (closure over current env), fun application (clause arity + pattern + guard filtering, fresh env per attempt), remote-call dispatch (`lists:*`, `io:*`, `erlang:*`). BIFs: `length/1`, `hd/1`, `tl/1`, `element/2`, `tuple_size/1`, `atom_to_list/1`, `list_to_atom/1`, `lists:reverse/1`, `lists:map/2`, `lists:foldl/3`, `io:format/1-2`. `io:format` writes to a capture buffer (`er-io-buffer`, `er-io-flush!`, `er-io-buffer-content`) and returns `ok` — supports `~n`, `~p`/`~w`/`~s`, `~~`. 35 new eval tests. Total eval 130/130; erlang suite 244/244. **Phase 2 complete — Phase 3 (processes, scheduler, receive) is next.**
 - **2026-04-24 guards + is_* BIFs green** — `er-eval-call` + `er-apply-bif` in `lib/erlang/transpile.sx` wire local function calls to a BIF dispatcher. Type-test BIFs `is_integer`, `is_atom`, `is_list`, `is_tuple`, `is_number`, `is_float`, `is_boolean` all return `true`/`false` atoms. Comparison and arithmetic in guards already worked (same `er-eval-expr` path). 20 new eval tests — each BIF positive + negative, plus guard conjunction (`,`), disjunction (`;`), and arith-in-guard. Total eval 95/95; erlang suite 209/209.
 - **2026-04-24 pattern matching green** — `er-match!` in `lib/erlang/transpile.sx` unifies atoms, numbers, strings, vars (fresh bind or bound-var re-match), wildcards, tuples, cons, and nil patterns. `case ... of ... [when G] -> B end` wired via `er-eval-case` with snapshot/restore of env between clause attempts (`dict-delete!`-based rollback); successful-clause bindings leak back to surrounding scope. 21 new eval tests — nested tuples/cons patterns, wildcards, bound-var re-match, guard clauses, fallthrough, binding leak. Total eval 75/75; erlang suite 189/189.
 - **2026-04-24 eval (sequential) green** — `lib/erlang/transpile.sx` (tree-walking interpreter) + `lib/erlang/tests/eval.sx`. 54/54 tests covering literals, arithmetic, comparison, logical (incl. short-circuit `andalso`/`orelse`), tuples, lists with `++`, `begin..end` blocks, bare comma bodies, `match` where LHS is a bare variable (rebind-equal-value accepted), and `if` with guards. Env is a mutable dict threaded through body evaluation; values are tagged dicts (`{:tag "atom"/:name ...}`, `{:tag "nil"}`, `{:tag "cons" :head :tail}`, `{:tag "tuple" :elements}`). Numbers pass through as SX numbers. Gotcha: SX's `parse-number` coerces `"1.0"` → integer `1`, so `=:=` can't distinguish `1` from `1.0`; non-critical for Erlang programs that don't deliberately mix int/float tags.