[Haskell-cafe] Advice for clean code.
jules at jellybean.co.uk
Tue Dec 4 08:05:44 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.
I don't think it's hugely important though.
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