Felipe Lessa wrote:
On Dec 4, 2007 1:28 AM, Don Stewart <[EMAIL PROTECTED]> 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 [1] 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.
Jules
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