How to [temporarily] suppress "defined but not used" warnings?

Question

When I prototype Haskell programs, I always get hundreds of warnings like this (not joking):

/Users/bob/SourceCode/course/is/expriment/LiftedSpine2.hs:70:15:
    Warning: Defined but not used: `ta'

/Users/bob/SourceCode/course/is/expriment/LiftedSpine2.hs:72:15:
    Warning: Defined but not used: `ta'

/Users/bob/SourceCode/course/is/expriment/LiftedSpine2.hs:77:26:
    Warning: Defined but not used: `v'

Is there anyway to remove these warnings temporarily? I tried putting this in my .hs file:

 {-# OPTIONS_GHC -fno-warn-unused-binds -fno-warn-name-shadowing 
    -fwarn-monomorphism-restriction -fwarn-hi-shadowing
 #-}

Unfortunately, it does not work, and although I also tried to :set -fno-warn-unused-binds, it still does not work.

Many thanks!

I really wish the `OPTIONS_GHC` thing did work, but haven't gotten around to following up with figuring out the exact behavior, filing a ticket, etc. — sclv, Nov 22 '11 at 19:01
Surprisingly nobody seems to have addressed the claims that OPTIONS_GHC doesn't work. I think the claim is false. The following works for me: {-# OPTIONS_GHC -Wall -fno-warn-unused-binds #-} — George Co, Jan 04 '20 at 15:32

score 36 · Accepted Answer · answered Nov 22 '11 at 10:13

36

Another possibility, depending on your situation: I believe you can prefix identifiers with an underscore to suppress this warning. So:

_x = 42

will not generate the warning if _x is not used.

answered Nov 22 '11 at 10:13

luqui

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Indeed. Why is that happening though? – Nikos Baxevanis Jan 18 '17 at 05:45
I think because somebody decided it should. Sometimes you want to document the meaning of a parameter even if you don't use It. – luqui Dec 06 '18 at 03:47

score 19 · Answer 2 · answered Sep 14 '13 at 09:41

19

GHC has two warnings flags which can trigger Warning: Defined but not used.

You need some combination of the command line flags -fno-warn-unused-binds and -fno-warn-unused-matches.

answered Sep 14 '13 at 09:41

liftM2

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If running `hdevtools` you have to prepend `-g` so that these work, like this: `hdevtools check -g-Wall -g-Wall -g-fno-warn-unused-binds -g-fno-warn-unused-matches source.hs` – Al.G. Jan 05 '17 at 11:29

score 8 · Answer 3 · answered Nov 22 '11 at 02:43

8

I usually use -w to suppress all warnings when I want get rid of some warning temporarily.

answered Nov 22 '11 at 02:43

augustss

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But then you lose out on other warnings you might've wanted to see. – Dan Burton Nov 22 '11 at 03:41
2

Yes, but when I temporarily remove warnings it's temporary, so I'll get to see those warnings soon enough. – augustss Nov 22 '11 at 03:45

score 5 · Answer 4 · answered Nov 22 '11 at 12:25

5

I use a workaround for this:

I compile without warnings, but then I use HLint tool to display warnings for me. HLint has facilities to turn warnings separately.

answered Nov 22 '11 at 12:25

nponeccop

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How to [temporarily] suppress "defined but not used" warnings?

4 Answers4

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