/prog/ - "Haskell is referentially transparent"

Name: Anonymous 2015-06-13 11:30

This means that functions really are mathematical functions, not horrible complex imperative procedures. So if x == y then f x == f y too. This allows us to use equational reasoning and math and the entirety of category theory as a resource to draw upon when programming

but thats wrong..

Prelude> let d x = 2*x :: Int
Prelude> minBound == maxBound
True
Prelude> d minBound == d maxBound
False

Name: Mentifex 2015-06-13 12:01

http://ai.neocities.org/AiSteps.html

Name: Anonymous 2015-06-13 14:16

Strange. I wonder why minBound and maxBound are in Eq.

Name: Anonymous 2015-06-14 19:45

That's because Int is bounded, you mongoloid.

Name: Anonymous 2015-06-14 19:48

>>1
What the fuck are you doing you donkey?

λ> (minBound :: Int) == (maxBound :: Int)
False
λ> d minBound == d maxBound
False

Name: Anonymous 2015-06-14 22:31

>>5
He's been bitten by the monomorphism restriction (Bounded a => a defaulted to () in ghci).

Doesn't happen outside of ghci:

$ cat anus.hs
val = minBound == maxBound

main = print val
$ runghc anus.hs

anus.hs:1:7:
    No instance for (Bounded a0) arising from a use of ‘minBound’
    The type variable ‘a0’ is ambiguous
    Note: there are several potential instances:
      instance Bounded () -- Defined in ‘GHC.Enum’
      instance (Bounded a, Bounded b) => Bounded (a, b)
        -- Defined in ‘GHC.Enum’
      instance (Bounded a, Bounded b, Bounded c) => Bounded (a, b, c)
        -- Defined in ‘GHC.Enum’
      ...plus 17 others
    In the first argument of ‘(==)’, namely ‘minBound’
    In the expression: minBound == maxBound
    In an equation for ‘val’: val = minBound == maxBound

anus.hs:1:16:
    No instance for (Eq a0) arising from a use of ‘==’
    The type variable ‘a0’ is ambiguous
    Note: there are several potential instances:
      instance Eq a => Eq (GHC.Real.Ratio a) -- Defined in ‘GHC.Real’
      instance Eq () -- Defined in ‘GHC.Classes’
      instance (Eq a, Eq b) => Eq (a, b) -- Defined in ‘GHC.Classes’
      ...plus 23 others
    In the expression: minBound == maxBound
    In an equation for ‘val’: val = minBound == maxBound
$

"Haskell is referentially transparent"

1 Name: Anonymous 2015-06-13 11:30

2 Name: Mentifex 2015-06-13 12:01

3 Name: Anonymous 2015-06-13 14:16

4 Name: Anonymous 2015-06-14 19:45