[Haskell] do notation and type synonym
tomasz.zielonka at gmail.com
Sun Aug 7 14:42:19 EDT 2005
On Sun, Aug 07, 2005 at 08:26:07PM +0200, mt wrote:
> the first check5 is ok and return Nothing while the second check5' will raise
> an "Exception: Non-exhaustive patterns" (which is what i've expected).
> the sentence "there is nothing magic with do" with its reason are important
> for me to understand monads and do notation, so maybe someone can rephrase
> "there is nothing magic with do" and explain the exposed behavior?
The actual translation is a bit more complex to deal with (surprise!)
pattern-match failures, like in your code. See the third equation in the
"Translation" border on this page:
Still no magic.
> second one:
> is it possible to write something like
> type Point = (Float, Float)
> type Vector = (Float, Float)
> and still have type safety (i.e. not be able to mix Point and Vector) (and
> still have (*,*) without constructor)?
I think it's not possible in current Haskell. If tuples were somehow
overloaded, as numbers are...
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