No blackbox found for: GHC.Integer.Type.gcdInteger

[bgamari]

It is very easy to stumble into this with realToFrac:

{-# LANGUAGE ScopedTypeVariables #-}

module Hi where

import Clash.Prelude

{-# ANN test
    ((defSyn "test")
             { t_name = "test"
             , t_inputs = [PortName "x"]
             , t_output = PortName "out"
             })
 #-}
test :: Signal System (SFixed 16 16)
     -> Signal System (SFixed 18 18)
test = fmap realToFrac

Admittedly, realToFrac is defined in terms of toRational . fromRational so this may be something just Clash just can't reasonably be expected to implement. Afterall, I suspect that resizeF would be a better replacement for realToFrac in most cases.