The set symmetric-difference operator >< is not parsed

• Type: feature (Pascal dialect surface) — Track P
• Found: 2026-08-09, an FPC differential over the set/record operator surface (Track A session). Everything else in that sweep matched FPC exactly: + * -, =, <=, >=, in, Include/Exclude, char sets, ranges, runtime-valued elements, 256-element sets, and records/arrays of records. >< is the one hole.

s1 := [1, 3, 5];
s2 := [3, 5, 7];
WriteLn(1 in (s1 >< s2));      { FPC: TRUE }

pascal26:25: error: expected expression
  near:   in  s1  >>>  s2

Shape of the fix

A lexer token for >< and one more arm in the set-binop lowering, which already has +/*/- through IR_SET_BINOP — symmetric difference is (a - b) + (b - a), or a per-word XOR at the same place the other three are emitted, which is cheaper and is what FPC does.

Filed under P (Pascal dialect surface) though the edit lands in the shared lexer.inc/parser.inc, so it obeys Track A's no-concurrent-edit rule. Low priority: >< is rare in real code, and the workaround (a - b) + (b - a) is exact.

Triage 2026-08-19 (Track D re-triage pass, pin v363) — ALREADY SOLVED, closing

Re-ran the ticket's own repro against the pinned compiler; it no longer reproduces. The quoted pascal26:25: error: expected expression is gone.

s1 := [1,3,5]; s2 := [3,5,7];
WriteLn(1 in (s1 >< s2));          { pxx: TRUE    FPC: TRUE }
s3 := s1 >< s2;
for i := 0 to 9 do if i in s3 then Write(i, ' ');
                                   { pxx: 1 7     FPC: 1 7  }

Both the membership form the ticket quotes and a full enumeration of the resulting set agree with FPC 3.x element for element, so the operator is not merely parsed — it lowers correctly. Landed incidentally in the weeks of operator/set work since 2026-08-09; no separate implementation is needed.

Closed as already solved, not as rejected.

Log

• 2026-08-19 — resolved, commit 0da3e73ce.