On Tue, Jan 20, 2015 at 1:36 PM, Volker Wysk <verteiler@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.)

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