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Made fromIntegerNat use case instead of if #4357

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Made fromIntegerNat use case instead of if #4357

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537ebcc
Made fromIntegerNat use `case` instead of `if`
SaraWolffs Feb 26, 2018
2ee99aa
Documented s/if/case/ in fromIntegerNat
Feb 26, 2018
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13 changes: 7 additions & 6 deletions libs/prelude/Prelude/Nat.idr
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Original file line number Diff line number Diff line change
Expand Up @@ -72,12 +72,13 @@ mult (S left) right = plus right $ mult left right

||| Convert an Integer to a Nat, mapping negative numbers to 0
fromIntegerNat : Integer -> Nat
fromIntegerNat 0 = Z
fromIntegerNat n =
if (n > 0) then
S (fromIntegerNat (assert_smaller n (n - 1)))
else
Z
fromIntegerNat i =
case (i > 0) of
True => S (fromIntegerNat (assert_smaller i (i - 1)))
False => Z
-- Using if here would cause infinite looping in some cases.
-- This could be fixed by redundantly matching on 0 explicitly, but that would stop
-- fromIntegerNat from reducing in proofs.

||| Convert a Nat to an Integer
toIntegerNat : Nat -> Integer
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