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Add HasCallStack where error can occur #235

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Add HasCallStack where error can occur #235

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2acff8d
Add HasCallStack where error can occur
dspies-leapyear Nov 27, 2018
e1b5aa2
Use Data.CallStack instead
dspies-leapyear Nov 29, 2018
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3 changes: 2 additions & 1 deletion Test/QuickCheck/Gen.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,7 @@ import Test.QuickCheck.Random
import Data.List
import Data.Ord
import Data.Maybe
import GHC.Stack (HasCallStack)

--------------------------------------------------------------------------
-- ** Generator type
Expand Down Expand Up @@ -197,7 +198,7 @@ frequency xs0 = choose (1, tot) >>= (`pick` xs0)
pick _ _ = error "QuickCheck.pick used with empty list"

-- | Generates one of the given values. The input list must be non-empty.
elements :: [a] -> Gen a
elements :: HasCallStack => [a] -> Gen a
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This only works with recent versions of GHC.

My call-stack package provides a shim for backwards compatibility. @nick8325 are you fine with adding that dependency? If yes, we could also add source locations to e.g. ===.

If not, we would want to CPP the HasCallStack => of the type signature.

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👍

elements [] = error "QuickCheck.elements used with empty list"
elements xs = (xs !!) `fmap` choose (0, length xs - 1)

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