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.
64 lines
1.8 KiB
Text
64 lines
1.8 KiB
Text
import Lean
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open Lean Parser Meta Elab Do
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set_option backward.do.legacy false
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syntax (name := myReturn) "myreturn" : doElem
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@[doElem_elab myReturn] def elabMyReturn : DoElab := fun _stx dec => do
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elabDoElem (← `(doElem| return 42)) dec
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/--
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error: No `ControlInfo` inference handler found for `myReturn` in syntax ⏎
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myreturn
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Register a handler with `@[doElem_control_info myReturn]`.
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-/
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#guard_msgs (error) in
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#eval Id.run do
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for i in [1, 2, 3] do
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myreturn
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return 0
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@[doElem_control_info myReturn] def controlInfoMyReturn : ControlInfoHandler := fun _stx => do
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return { numRegularExits := 0, returnsEarly := true }
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/-- info: 42 -/
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#guard_msgs in
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#eval Id.run do
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for i in [1, 2, 3] do
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myreturn
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return 0
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syntax (name := myIf) "myif" term " then" doSeq " else" doSeq : doElem
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@[doElem_elab myIf] def elabMyIf : DoElab := fun stx dec => do
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let `(doElem| myif $cond:term then $thenSeq else $elseSeq) := stx | throwUnsupportedSyntax
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elabDoElem (← `(doElem| if $cond then $thenSeq else $elseSeq)) dec
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/--
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error: No `ControlInfo` inference handler found for `myIf` in syntax ⏎
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myif i > 1 then
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return 23 else
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continue
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Register a handler with `@[doElem_control_info myIf]`.
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-/
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#guard_msgs (error) in
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#eval Id.run do
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for i in [1, 2, 3] do
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myif i > 1 then return 23 else continue
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return 0
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@[doElem_control_info myIf] def controlInfoMyIf : ControlInfoHandler := fun stx => do
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let `(doElem| myif $_:term then $thenSeq else $elseSeq) := stx | throwUnsupportedSyntax
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let thenInfo ← inferControlInfoSeq thenSeq
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let elseInfo ← inferControlInfoSeq elseSeq
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return thenInfo.alternative elseInfo
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/-- info: 26 -/
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#guard_msgs in
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#eval Id.run do
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let mut x := 0
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for i in [1, 2, 3] do
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myif i > 2 then return x + 23 else x := x + i; continue
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return 0
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