Hello Volker, All identifiers prefixed with an underscore are "typed holes", see: https://downloads.haskell.org/~ghc/7.8.3/docs/html/users_guide/typed-holes.h... Edward Excerpts from Volker Wysk's message of 2015-01-20 10:36:09 -0800:
Hello!
What is a "hole"?
This program fails to compile:
main = _exit 0
I get this error message:
ex.hs:1:8: Found hole ‘_exit’ with type: t Where: ‘t’ is a rigid type variable bound by the inferred type of main :: t at ex.hs:1:1 Relevant bindings include main :: t (bound at ex.hs:1:1) In the expression: _exit In an equation for ‘main’: main = _exit
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.
Bye Volker