[Haskell-cafe] Why were unfailable patterns removed and "fail" added to Monad?

Dan Doel dan.doel at gmail.com
Fri Jan 20 05:11:55 CET 2012

On Thu, Jan 19, 2012 at 10:43 PM, Gregory Crosswhite
<gcrosswhite at gmail.com> wrote:
> first, that the notion of "unfailable" was not removed from the language
> so much as not added in the first place

No, this is not correct. Unfailable patterns were specified in Haskell
1.4 (or, they were called "failure-free" there; they likely existed
earlier, too, but I'll leave the research to people who are
interested). They were "new" in the sense that they were introduced
only for the purposes of desugaring do/comprehensions, whereas
refutable vs. irrefutable patterns need to be talked about for other

-- Dan

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