"Found hole"

Merijn Verstraaten merijn at inconsistent.nl
Wed Jan 21 10:03:38 UTC 2015

Typed holes is not an extension, because it's considered a warning/error. The reason for this is that code with typed holes is NOT valid haskell to begin with, therefore the behaviour doesn't conflict with any description in the report.

Additionally, the ability to disable the typed holes warning is disappearing in 7.10 (well, sorta, you can silence them, but you can't get the "old" error message back). If there's any comments on how to improve the warning message to be less confusing I'd be interested to hear them.


> On 20 Jan 2015, at 19:44, Brandon Allbery <allbery.b at gmail.com> wrote:
> On Tue, Jan 20, 2015 at 1:36 PM, Volker Wysk <verteiler at volker-wysk.de> wrote:
> What is a "hole"?
> https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/typed-holes.html
> When I replace "_exit" with "foo", it produces a "not in scope" error, as
> expected. What is special about "_exit"? It doesn't occur in the Haskell
> Hierarchical Libraries.
> The leading underscore invokes the typed holes extension. If you want to use such names, you'll need {-# LANGUAGE NoTypedHoles #-} as the first line of the source file. (I am not sure why this extension was enabled by default.)
> --
> brandon s allbery kf8nh                               sine nomine associates
> allbery.b at gmail.com                                  ballbery at sinenomine.net
> unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net
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