class - What's the difference between "float" and "fractional" in Haskell? - 


prelude> let c=[1.0,2.0] prelude> :t c c :: fractional t => [t]

i'd expect "c" list of either num or float. why fractional? there implicit type conversion going on here in haskell?

you can make happen:

> :set -xnumdecimals > let c=[1.0,2.0] > :t c c :: num t => [t]

the answer "why fractional" "because report says so":

float →   decimal . decimal [exponent]       |   decimal exponent

a floating literal stands application of fromrational value of type rational (that is, ratio integer). given typings:

frominteger  :: (num a) => integer ->   fromrational :: (fractional a) => rational ->

integer , floating literals have typings (num a) => a , (fractional a) => a, respectively.

i guess report says because nice simple rule explain: no dot/exponent, it's num-polymorphic, yes dot/exponent, it's fractional-polymorphic.

two relevant bits are:
https://www.haskell.org/onlinereport/haskell2010/haskellch2.html#x7-190002.5
https://www.haskell.org/onlinereport/haskell2010/haskellch6.html#x13-1360006.4.1


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