4278038940
This PR adds a new, extensible `do` elaborator. Users can opt into the new elaborator by unsetting the option `backward.do.legacy`. New elaborators for the builtin `doElem` syntax category can be registered with attribute `doElem_elab`. For new syntax, additionally a control info handler must be registered with attribute `doElem_control_info` that specifies whether the new syntax `return`s early, `break`s, `continue`s and which `mut` vars it reassigns. Do elaborators have type ``TSyntax `doElem → DoElemCont → DoElabM Expr``, where `DoElabM` is essentially `TermElabM` and the `DoElemCont` represents how the rest of the `do` block is to be elaborated. Consult the docstrings for more details. Breaking Changes: * The syntax for `let pat := rhs | otherwise` and similar now scope over the `doSeq` that follows. Furthermore, `otherwise` and the sequence that follows are now `doSeqIndented` in order not to steal syntax from record syntax. Breaking Changes when opting into the new `do` elaborator by unsetting `backward.do.legacy`: * `do` notation now always requires `Pure`. * `do match` is now always non-dependent. There is `do match (dependent := true)` that expands to a term match as a workaround for some dependent uses.
19 lines
642 B
Text
19 lines
642 B
Text
example : Except String Nat := do
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try
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-- The try block has result type Unit:
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pure ()
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catch _ =>
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-- The doLetElse here should not "eat" the `return 42` as its body seq.
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-- If it does, we'd get a type error because the result type is not Unit.
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let .some true := none | throw "error"
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return 42
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example : Except String Nat := do
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try
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-- The try block has result type Unit:
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pure ()
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catch _ =>
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-- The doLetArrow here should not "eat" the `return 42` as its body seq.
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-- If it does, we'd get a type error because the result type is not Unit.
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let .some true ← pure none | throw "error"
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return 42
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