On Tue, Mar 10, 2015 at 8:21 AM, Lyndon Maydwell
GHC 7.8.3 here.
Hmm, on second inspection I believe that the Bool reference is to the top-level expression, not the list items after all.
I don't seem to get any defaulting behaviour either when not using GHCi. This seems to indicate that the extended interactive type defaulting is coming into play:
https://downloads.haskell.org/~ghc/7.8.2/docs/html/users_guide/interactive-e...
I'd guess that this means that the () default is being used. -Wall seems to indicate that this is in-fact the case:
[Prelude] λ [] == []
<interactive>:2:4: Warning: Defaulting the following constraint(s) to type ‘()’ (Eq t0) arising from a use of ‘==’ In the expression: [] == [] In an equation for ‘it’: it = [] == [] True
Hope this helps.
Thats better -- thanks Lyndon! So after some fishing around I find the more pointed warning I am after is -fwarn-type-defaults The docs seem confusing though: https://downloads.haskell.org/~ghc/7.4.1/docs/html/users_guide/options-sanit... Under -fwarn-type-defaults: says *Have the compiler warn/inform you where in your source the Haskell defaulting mechanism for numeric types kicks in.* Wheres the numeric here?