ghci - defaulting confusion

Question

I happened to see some strange behaviour during checking the size (minBound,maxBound) and \"length in decimal representation\" of different integra

Answer 1

Confusingly, this is still the monomorphism restriction at play (or rather the lack thereof when in GHCi). Since GHCi doesn't have the monomorphism restriction enabled, your definitions of mi and ma don't get specialized to Int as you think they will - instead they stay general as mi, ma :: Bounded a => a and the a variable gets instantiated twice

• once as () in fromIntegral $ length $ show ma (as you observed, this is a default)
• once as Int in [mi,ma,le] :: [Int]

If you want mi and ma to actually be of type Int, annotate them as such directly

Prelude> :{
Prelude| let mi, ma :: Int
Prelude|     mi = minBound
Prelude|     ma = maxBound
Prelude|     le = fromIntegral $ length $ show ma
Prelude|  in [mi,ma,le]
Prelude| :}
[-9223372036854775808,9223372036854775807,19]

Or turn on the monormorphism restriction manually in GHCi

Prelude> :set -XMonomorphismRestriction
Prelude> :{
Prelude| let mi = minBound
Prelude|     ma = maxBound
Prelude|     le = fromIntegral $ length $ show ma
Prelude| in [mi,ma,le] :: [Int]
Prelude| :}
[-9223372036854775808,9223372036854775807,19]