[Haskell-beginners] Data structure for Propositional Logic formulas

[Christian Maeder]

Am 12.10.2011 23:24, schrieb Benedict Eastaugh:
> Hi Alex,
>
> since Daniel has done a nice job of actually answering your questions,
> I shall just note that I have a module similar to this available on
> Hackage as part of my hatt package, which generates truth tables for
> formulae in classical propositional logic.
>
> http://hackage.haskell.org/package/hatt
> http://hackage.haskell.org/packages/archive/hatt/1.3.0/doc/html/Data-Logic-Propositional.html

Why do most people like duplicate or repeated code?

Instead of

data Expr = Variable      String
           | Negation      Expr
           | Conjunction   Expr Expr
           | Disjunction   Expr Expr
           | Conditional   Expr Expr
           | Biconditional Expr Expr

you are usually better served by:

data Expr = Variable      String
           | Negation      Expr
           | Junct BinOp   Expr Expr

data BinOp = Conjunction | Disjunction | Conditional | Biconditional

Cheers Christian

>
> Benedict
>