Question

Could anybody explain this output to me? Im completely new at Haskell and do not know why that happens.

import Data.Char

o=ord 'f'

main=do print (o==102)
    print (mod (102^2087) 9797)
    print (mod (o^2087) 9797)

Output:

xxx:~/Arbeitsfläche$ runhaskell st.hs
True
5253
0

GHC version 7.4.1, Ubuntu

Answer 1

This is because o has type Int which has a limited range and thus (mod (o^2087) 9797) is also an Int. However, the constant 102 is of a generic numeric type (Num a => a) and (mod (102^2087) 9797) is of generic integral type (Integral a => a). When this generic integral type must be resolved to a concrete type, which happens when applying print, the default resolution is to choose Integer, an unbounded integral type. The details of this resolution are described in section 4.3.4 Ambiguous Types, and Defaults for Overloaded Numeric Operations of the Haskell 2010 Report.