Reduce Eclipse (type) warning level

Question

I recently installed the Haskell Eclipse-plugin "EclipseFP". Everything works pretty well while there's one feature which makes me very angry hehe. I cannot reduce the warning level of the output. Eclipse/It's plugin seems to auto-append the "-Wall" flag, which is very very sensitive against type-things. Let's show this on an example:

*Main> head [1,2,3]

<interactive>:1:11:
    Warning: Defaulting the following constraint(s) to type `Integer'
               (Num a0) arising from the literal `3'
    In the expression: 3
    In the first argument of `head', namely `[1, 2, 3]'
    In the expression: head [1, 2, 3]

<interactive>:1:11:
    Warning: Defaulting the following constraint(s) to type `Integer'
               (Num a0) arising from the literal `3' at <interactive>:1:11
               (Show a0) arising from a use of `print' at <interactive>:1:1-12
    In the expression: 3
    In the first argument of `head', namely `[1, 2, 3]'
    In the expression: head [1, 2, 3]
1
*Main>

Yep, that is REALLY annoying. It's caused by "intrinsic" functions as well as on custom ones. Another one:

factorial :: (Integral a) => a -> a
factorial 1 = 1
factorial n = n * factorial (n-1)

*Main> factorial 3

<interactive>:1:1:
    Warning: Defaulting the following constraint(s) to type `Integer'
               (Integral a0) arising from a use of `factorial'
                             at <interactive>:1:1-9
               (Num a0) arising from the literal `3' at <interactive>:1:11
    In the expression: factorial 3
    In an equation for `it': it = factorial 3

<interactive>:1:1:
    Warning: Defaulting the following constraint(s) to type `Integer'
               (Integral a0) arising from a use of `factorial'
                             at <interactive>:1:1-9
               (Num a0) arising from the literal `3' at <interactive>:1:11
               (Show a0) arising from a use of `print' at <interactive>:1:1-11
    In the expression: factorial 3
    In an equation for `it': it = factorial 3
6
*Main>

How would you actually write this code so the warning doesn't show up in the first place? — Gerold Meisinger, May 29 '12 at 20:11

score 6 · Accepted Answer · answered Jan 26 '12 at 18:38

6

I don't know about Eclipse, but you can off warnings in your .ghci file. Put

:set -Wall           -- unnecessary if Eclipse already turns it on
:set -fno-warn-type-defaults
:set -fno-warn-unused-do-bind

and whatever else you don't want to warned about by default into your ~/.ghci and reduce the warnings to the important ones. If you want to load some modules by default, you can also add import Control.Applicative (or whichever).

answered Jan 26 '12 at 18:38

Daniel Fischer

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Thanks, that did the job. Note that on windows, the path would be C:\Users\\AppData\Roaming\ghc\ghci.conf - Create the file and copy the above if the file does not exist, yet. – poitroae Jan 26 '12 at 19:46

score 5 · Answer 2 · answered May 29 '12 at 20:10

5

in .cabal file write: ghc-options: -Wall -fno-warn-type-defaults -fno-warn-unused-do-bind

answered May 29 '12 at 20:10

Gerold Meisinger

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score 2 · Answer 3 · edited May 23 '17 at 10:28

There is a way to put those commands suggested by Daniel Fischer right in EclipseFP.

Open "Run Configurations...", select yours, switch to "Automation" tab, type in a command in the text edit. Unfortunately, it's a one-line edit entry and GHCI doesn't support several commands in one line.

However, you can type multi-line text somewhere and paste it in this text edit so that it will look like :set -fno-warn-type-defaults[000A]:set -fno-warn-unused-do-bind.

There is also a special multi-line text edit named "Arguments" but it doesn't solve the problem since these arguments are inserted before that -Wall, that's why they don't make sense.

It is Okay to put two options on one set command like :set -fno-warn-type-defaults -fno-warn-unused-do-bind — The_Ghost, Oct 25 '12 at 16:27

score 1 · Answer 4 · answered Aug 09 '13 at 10:40

Another approach, instead of adding arguments to switch off this behaviour, is to prevent it being switched on in the first place.

Inside the Eclipse haskell project, there is a file called eclispeProjectName.cabal. This is where the -Wall ghci argument is defined. Comment out that line.

For example: in an eclipse haskell project called haskelltest, there is a file called haskelltest.cabal at the top level of the project. Set its contents like below - see the last line where I've commented out the ghc-options setting:

name:           haskelltest
version:        0.1
cabal-version:  >=1.2
build-type:     Simple
author:         marty

executable haskelltest
  hs-source-dirs:  src
  main-is:         Main.hs
  build-depends:   base >= 4
--  ghc-options:     -Wall

BTW Apparently turning off the -Wall setting is considered bad practise. See [link](http://stackoverflow.com/questions/4174629/impact-on-style-of-ghc-wall) so lambdor's approach is probably better. — Martin Devlin, Aug 09 '13 at 10:51

Reduce Eclipse (type) warning level

4 Answers4