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fix(parser): resolve state-41 effect-row MINUS/ARROW S/R conflict (75→72) [#215 family A] #216

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Merged
hyperpolymath merged 1 commit into from
May 18, 2026
Merged

fix(parser): resolve state-41 effect-row MINUS/ARROW S/R conflict (75→72) [#215 family A] #216

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16 changes: 15 additions & 1 deletion lib/parser.mly
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Original file line number Diff line number Diff line change
Expand Up @@ -83,6 +83,20 @@ let rec effect_union_of_list = function
%token EOF

/* Precedence (lowest to highest) */
/* `LOWEST_TYPE_ARROW` is a pseudo-token (never lexed) carrying the
lowest precedence. It tags the base `type_expr_arrow -> type_expr_primary`
reduction so that in state 41 — after a `type_expr_primary`, lookahead
`ARROW` (continue an arrow type) or `MINUS` (open the legacy `-{E}->`
effect row) — the parser SHIFTS rather than reducing the base case.
Shift was already Menhir's (correct) arbitrary resolution there (a
bare type can never be followed by `->`/`-{` *and* want to stop), so
declaring this precedence is parse-behaviour-preserving and only
silences the spurious conflict. `ARROW` has no precedence elsewhere
and is a conflict lookahead ONLY in state 41 (verified via
`menhir --explain`), so giving it precedence here is side-effect-free.
See affinescript#215 (family A). */
%nonassoc LOWEST_TYPE_ARROW
%nonassoc ARROW
%right EQ PLUSEQ MINUSEQ STAREQ SLASHEQ
%left PIPEPIPE
%left AMPAMP
Expand Down Expand Up @@ -416,7 +430,7 @@ type_expr_arrow:
past the closing RPAREN. */
| LPAREN ty1 = type_expr COMMA tys = separated_nonempty_list(COMMA, type_expr) RPAREN ARROW ret = type_expr_arrow
{ List.fold_right (fun p acc -> TyArrow (p, None, acc, None)) (ty1 :: tys) ret }
| ty = type_expr_primary { ty }
| ty = type_expr_primary %prec LOWEST_TYPE_ARROW { ty }

type_expr_primary:
| LPAREN RPAREN { TyTuple [] }
Expand Down
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