28 lines
536 B
Text
28 lines
536 B
Text
#lang lean4
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def foo (x : Nat) : IO Bool := do
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if x == 0 then
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throw $ IO.userError "foo: unexpected zero"
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pure (x == 1)
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def tst (x : Nat) : IO Unit := do
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if x == 0 then
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IO.println "x is 0"
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else if (← foo x) then
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IO.println "x is 1"
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else
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IO.println "other"
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#eval tst 0
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#eval tst 1
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#eval tst 2
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syntax term "<|||>" term : doElem
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macro_rules
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| `(doElem| $a:term <|||> $b:term) => `(doElem| if (← $a:term) then pure true else $b:term)
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def tst2 : IO Bool := do
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pure true <|||> (← throw $ IO.userError "failed")
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#eval tst2
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