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.
41 lines
1.1 KiB
Text
41 lines
1.1 KiB
Text
set_option backward.do.legacy false
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-- Refines the free variable `n` and the result type of the `do` block:
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example (x : Nat) (n : Fin (x + 1)) : Id (Fin (x + 1)) := do
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match (dependent := true) x with
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| 42 => pure 40
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| _ => pure n
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-- Just refines the free variable `n`:
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example (x : Nat) (n : Fin x) : Id Bool := do
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match (dependent := true) x with
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| 0 => n.elim0
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| _ => pure true
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/--
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error: Dependent match is not supported when the result type of the `do` block ⏎
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Bool
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is different to the result type of the `match` ⏎
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Fin (x + 1)
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-/
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#guard_msgs (error) in
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example (x : Nat) (n : Fin (x + 1)) : Id Bool := do
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let y : Fin (x + 1) ←
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match (dependent := true) x with
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| 42 => pure 40
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| _ => pure 0
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return y % 2 == 0
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/--
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error: Dependent match is not supported when the result type of the `do` block ⏎
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Bool
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is different to the result type of the `match` ⏎
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?m.7
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-/
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#guard_msgs (error) in
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example (x : Nat) (n : Fin (x + 1)) : Id Bool := do
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let y ←
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match (dependent := true) x with
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| 42 => pure 40
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| _ => pure 0
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return y % 2 == 0
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