Re: [Haskell-beginners] Re: Boilerplate Code

4 Aug 2010

      Kyle Murphy schrieb:
[...]
...
typeChecker a b = toConstr a == toConstr b
Right, that is (slightly) cleaner than using my "show" trick below.
...
On Tue, Aug 3, 2010 at 13:51, Alex Rozenshteyn
                mailto:rpglover64@gmail.com> wrote:
That is a dirty, dirty hack.
[...]

Alternatively you could define your own enumeration type:

  data SchemeType = NumberT | BoolT | AtomT
    deriving Eq

  schemeTypeOf :: SchemeVal -> SchemeType
  schemeTypeOf v = case v of
    Number _ -> NumberT
    Bool _ -> BoolT
    Atom _ -> AtomT

  typeChecker = Data.Function.on (==) schemeTypeOf

C.
...
>
                        > numberP :: SchemeVal -> SchemeVal
                        > numberP (Number _) = Bool True
                        > numberP _          = Bool False
                        >
                        > boolP :: SchemeVal -> SchemeVal
                        > boolP (Bool _) = Bool True
                        > boolP _        = Bool False
                        >
                        > symbolP :: SchemeVal -> SchemeVal
                        > symbolP (Atom _) = Bool True
                        > symbolP _        = Bool False
[...]
...
typeChecker s1 s2 = let f = takeWhile isAlphaNum
                        . show in
                          Bool $ f s1 == f s2
hoping that my "f" just extracts the constructor
                        as string.

Re: [Haskell-beginners] Re: Boilerplate Code

Christian Maeder