$ cat foo.hs
something = to be done
x = x + 1
wat = x "¯\\_(ツ)_/¯"
main = print "hi"
$ ghc --make -O foo -fdefer-type-errors && echo sucesfuly compoiled && ./foo
[1 of 1] Compiling Main ( foo.hs, foo.o )
foo.hs:2:13: warning: [-Wdeferred-out-of-scope-variables]
Variable not in scope: to :: t1 -> t2 -> t
|
2 | something = to be done
| ^^
foo.hs:2:16: warning: [-Wdeferred-out-of-scope-variables]
Variable not in scope: be
|
2 | something = to be done
| ^^
foo.hs:2:19: warning: [-Wdeferred-out-of-scope-variables]
Variable not in scope: done
|
2 | something = to be done
| ^^^^
Linking foo ...
sucesfuly compoiled
"hi"
$
Haskell also has typed holes (with a similar -fdefer-typed-holes) since 7.10. I've described it in slightly more detail here in a previous post in this thread [0].
Typed holes (but not the defer- option) have been enabled by default for some time now. They're an immediate go-to when scratching my head over types. I prefer them to the type error output, not only because they give better suggestions, but also because they can be named (_a, _conversionFunction, etc).
