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33 lines
894 B
Idris
33 lines
894 B
Idris
data IsS : (Nat -> Nat) -> Type where
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Indeed : (s : Nat -> Nat) -> s === S -> IsS s
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------------------------------------------------------------------------
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-- 1.
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-- the S pattern is forced by the fact the parameter is instantiated
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-- so everything is fine
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-- either left implicit
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indeed : IsS S -> S === S
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indeed (Indeed _ eq) = eq
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-- or made explicit
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indeed2 : IsS S -> S === S
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indeed2 (Indeed S eq) = eq
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------------------------------------------------------------------------
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-- 2. The S pattern is not forced by the parameter (a generic variable)
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-- either don't match on it
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indeed3 : IsS s -> s === S
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indeed3 (Indeed s eq) = eq
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-- or match on the proof that forces it
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indeed4 : IsS s -> s === S
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indeed4 (Indeed S Refl) = Refl
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-- ^ forced by Refl
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-- If you don't: too bad!
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fail : IsS s -> s === S
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fail (Indeed S eq) = eq
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-- ^ not Refl, S not forced! OUCH
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