[Haskell-cafe] Advice for clean code.
dons at galois.com
Tue Dec 4 12:07:13 EST 2007
> Felipe Lessa wrote:
> >On Dec 4, 2007 1:28 AM, Don Stewart <dons at galois.com> wrote:
> >> -- How to display results
> >> instance Show Action where
> >> show MoveOutOfBounds = "Sorry you can't move in that
> >> direction."
> >> show (MoveBadTerrain a) = case a of
> >> Wall -> "You walk into a wall."
> >> Tree -> "There is a tree in the
> >> way."
> >> otherwise -> "You can't move there."
> >> show MoveOk = "Good move."
> >I always thought show was meant for returning a String that could be
> >used to recreate the original data if you copy-pasted it in your code
> >or if you used read (i.e. read . show == id). Reading the
> >documentation more carefully, I see that  says that this property
> >holds for *derived* instances, and says nothing about it in the
> >general case.
> I would not write what dons wrote.
> I would have a custom function here rather than "misusing" Show in this
> way; call it "showMoveError" or similar. For mostly the reasons Felipe gave.
Yes, this is considered bad practice in larger project (not so much in
little hacks), since read . show should hold, as should the 'paste'
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