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fix(parser): remove duplicate [T] array-sugar production (kills never-reduced + 26 R/R conflicts) #214

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Merged
hyperpolymath merged 1 commit into from
May 18, 2026
+8 −13
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fix(parser): remove duplicate [T] array-sugar production (kills never-reduced + 26 R/R conflicts) #214

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21 changes: 8 additions & 13 deletions lib/parser.mly
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Original file line number Diff line number Diff line change
Expand Up @@ -437,9 +437,14 @@ type_expr_primary:
LT/GT tokens are shared with expression-position less-than. */
| name = upper_ident LT args = separated_nonempty_list(COMMA, type_arg) GT
{ TyApp (mk_ident name $startpos(name) $endpos(name), args) }
/* Array sugar: [T] desugars to Array[T] (issues-drafts/02). The element
type can be any type_expr (recursive), so [[Int]] means Array[Array[Int]]
and [Result[T, E]] works as expected. */
/* Array sugar: `[T]` desugars to `Array[T]` (issues-drafts/02; #40). The
element type can be any type_expr (recursive), so `[[Int]]` means
Array[Array[Int]] and `[Result[T, E]]` works as expected. This is the
syntax stdlib has used all along (`fn map<T, U>(arr: [T], ...)`). The
typechecker (lib/typecheck.ml ~724, 813, 1024) canonicalises array
literals/operations on `TApp (TCon "Array", ...)`, so `Array` is the
right desugar target — `List` here would trigger a
`Unify.TypeMismatch (List, Array)` at check time. */
| LBRACKET elem = type_expr RBRACKET
{ TyApp (mk_ident "Array" $startpos $endpos, [TyArg elem]) }
/* Function-type-as-type: `fn(A, B) -> C` lowers to the curried arrow
Expand All @@ -458,16 +463,6 @@ type_expr_primary:
the interior in one pass without lookahead conflicts. */
| LBRACE body = ty_record_body RBRACE
{ TyRecord (fst body, snd body) }
/* Array shorthand: `[T]` desugars to `Array[T]`. This is the syntax
stdlib has used all along (`fn map<T, U>(arr: [T], f: T -> U) -> [U]`,
`Result[[T], E]`, etc.) but it was previously only accepted in stdlib
load paths, not in user source. The typechecker (lib/typecheck.ml
lines 724, 813, 1024) canonicalises array literals/operations on
`TApp (TCon "Array", ...)`, so `Array` is the right desugar target —
using `List` here triggers a `Unify.TypeMismatch (List, Array)` at
check time. Closes #40. */
| LBRACKET ty = type_expr RBRACKET
{ TyApp (mk_ident "Array" $startpos $endpos, [TyArg ty]) }
/* Built-in types */
| NAT { TyCon (mk_ident "Nat" $startpos $endpos) }
| INT_T { TyCon (mk_ident "Int" $startpos $endpos) }
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