tcfail153.hs:6:9: error:
• Couldn't match expected type ‘Bool’ with actual type ‘a’
‘a’ is a rigid type variable bound by
the type signature for:
f :: forall a. a -> [a]
at tcfail153.hs:5:1-13
• In the first argument of ‘g’, namely ‘x’
In the expression: g x
In an equation for ‘f’:
f x
= g x
where
g y = if y then [] else [...]
• Relevant bindings include
x :: a (bound at tcfail153.hs:6:3)
f :: a -> [a] (bound at tcfail153.hs:6:1)