On 13/01/14 18:42, Krzysztof Gogolewski wrote:
Hello,
As discussed on ghc-devs, I propose to enable -XTypeHoles in GHC by default. Rationale:
(1) This way holes are far easier to use; just entering "_" allows to check type of a subexpression, no need of adding "-XTypeHoles".
(2) This affects error messages only; i.e. the set of programs that compile stays the same - Haskell 2010. The only exception is that if you use -fdefer-type-errors, then a program with a hole compiles, but this seems fine with philosophy of -fdefer-type-errors.
If so: would you like it to be in 7.8 or wait a cycle? My preference is 7.8, two people (John and Richard) suggested 7.10.
-KG
Sounds good. Are there plans to allow TypeHoles to actually sit in place of types? In the past I did ``` data Hole hole :: Hole hole = undefined foo :: Integer -> Integer foo x = hole bar :: Integer -> Hole bar x y = x + y ``` to cause type errors that could guide me. I now don't have to resort to the first use in ‘foo’ but I still have to define my own Hole type in ‘bar’. -- Mateusz K.