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| 1 | namespace Syntax.Trees.Expressions is | |
| 2 | ||
| 3 | use Source | |
| 4 | ||
| 5 | // `type_expression` is the optional explicit type argument: `_[T]`. | |
| 6 | // Null for a bare `_`, whose type is supplied by the context. | |
| 7 | class DEFAULT(location: LOCATION, type_expression: TypeExpressions.TypeExpression?): Expression is | |
| 8 | // Constraint pushed in by the parent context (assignment RHS, | |
| 9 | // return position, typed `let` initializer, call argument). | |
| 10 | // For a bare `_` this is what gives it its type. | |
| 11 | ||
| 12 | super(location) | |
| 13 | ||
| 14 | // An untyped `_` can stand in for a discard formal in a | |
| 15 | // lambda's parameter group (`(_, b) => ...`, `_ => ...`): the | |
| 16 | // group is parsed as a tuple expression first and reinterpreted | |
| 17 | // as a pattern when the `=>` arrives, so `_` must round-trip | |
| 18 | // back into a discard binding leaf here. declare-members renames | |
| 19 | // the `_` name to a unique slot the way it does any other | |
| 20 | // discard. `_[T]` has no reading as a formal — a formal's type | |
| 21 | // comes from the `: T` syntax, not from `[T]`. | |
| 22 | awaits_context_type: bool => !type_expression? | |
| 23 | ||
| 24 | could_be_formal_argument: bool => !type_expression? | |
| 25 | ||
| 26 | try_copy_as_variable_left() -> Variables.VariableLeft? => | |
| 27 | if !could_be_formal_argument then | |
| 28 | null | |
| 29 | else | |
| 30 | Variables.SIMPLE_VARIABLE_LEFT(location, Identifiers.Identifier(location, "_")) | |
| 31 | fi | |
| 32 | ||
| 33 | try_copy_as_variable() -> VARIABLE? => | |
| 34 | if !could_be_formal_argument then | |
| 35 | null | |
| 36 | else | |
| 37 | VARIABLE(location, Identifiers.Identifier(location, "_"), TypeExpressions.INFER(location), null) | |
| 38 | fi | |
| 39 | ||
| 40 | set_expected_type(expected_type: Semantic.Types.Type?, error_message: string?) is | |
| 41 | compile_expressions_state.set_expected_type(expected_type, error_message) | |
| 42 | si | |
| 43 | ||
| 44 | accept(visitor: Visitor) is | |
| 45 | visitor.visit(self) | |
| 46 | si | |
| 47 | ||
| 48 | walk(visitor: Visitor) is | |
| 49 | if !visitor.pre(self) then | |
| 50 | if type_expression? then | |
| 51 | type_expression.walk(visitor) | |
| 52 | fi | |
| 53 | fi | |
| 54 | ||
| 55 | accept(visitor) | |
| 56 | si | |
| 57 | si | |
| 58 | si |