[Haskell-cafe] Enable -Wall by default?

[Henning Thielemann]

On Thu, 10 Dec 2020, Fumiaki Kinoshita wrote:

> [0] https://www.snoyman.com/blog/2020/12/haskell-bad-parts-3

He's pretty right about pattern matching and -Wall and 
-Wincomplete-uni-patterns and -Wpartial-fields. It's surprising that the 
two latter ones are not part of -Wall. But this is not your proposal.

I have always -Wall on, especially during early development. I can ignore 
warnings. But I will always remove the cause for warnings before making a 
commit. Warnings remind me on the unfinished bits. Thus also warnings 
about unused imports, unused parameters, unused functions are very 
important for me.

I would even like to see some warnings before or along type errors. 
Currently warnings are shown only after the type errors are resolved. 
However, sometimes I get very complicated type errors but actually the 
warning "variable x unused" (and thus type inference could not take place) 
would be much more helpful.

I have also taught programming to students. They often like to first run 
and test their programs and then resolve warnings somewhen in the future 
(or not at all). They are surprised why their programs don't work, whereas 
the warnings would directly point them to the problems. But -Wall is 
disabled by default. And thus making code warning free looks like an 
optional extra.

On the other hand I do not know how GHC with -Wall as default affects the 
tons of packages that are already released.