Ambiguous occurrence ‘stdout’, and likewise ‘stderr’, when trying to doctest turtle script

[reuleaux]

usually I run doctests on my Haskell programs, like so:

$ doctest -DDOCTEST somefile.hs

when I do this with a minimal turtle script, like this one:

#!/usr/bin/env runturtle

{-# LANGUAGE CPP #-}


#ifdef DOCTEST
-- stuff here usually
#endif


import Turtle

main = return ()

(having defined a separate runturtle script for that matter)

#!/bin/sh
exec cabal exec runhaskell -- "$@"

I get error messages:

rx@mirabelle {master} ~/cfg/spin $ doctest -DDOCTEST somefile.hs 

<interactive>:5:14: error:
    Ambiguous occurrence ‘stdout’
    It could refer to either ‘Turtle.stdout’,
                             imported from ‘Turtle’ at somefile.hs:12:1-13
                             (and originally defined in ‘Turtle.Prelude’)
                          or ‘System.IO.stdout’,
                             imported from ‘System.IO’
                             (and originally defined in ‘GHC.IO.Handle.FD’)

<interactive>:5:21: error:
    Ambiguous occurrence ‘stderr’
    It could refer to either ‘Turtle.stderr’,
                             imported from ‘Turtle’ at somefile.hs:12:1-13
                             (and originally defined in ‘Turtle.Prelude’)
                          or ‘System.IO.stderr’,
                             imported from ‘System.IO’
                             (and originally defined in ‘GHC.IO.Handle.FD’)

<interactive>:7:15: error:
    Ambiguous occurrence ‘stdout’
    It could refer to either ‘Turtle.stdout’,
                             imported from ‘Turtle’ at somefile.hs:12:1-13
                             (and originally defined in ‘Turtle.Prelude’)
                          or ‘System.IO.stdout’,
                             imported from ‘System.IO’
                             (and originally defined in ‘GHC.IO.Handle.FD’)

<interactive>:9:15: error:
    Ambiguous occurrence ‘stderr’
    It could refer to either ‘Turtle.stderr’,
                             imported from ‘Turtle’ at somefile.hs:12:1-13
                             (and originally defined in ‘Turtle.Prelude’)
                          or ‘System.IO.stderr’,
                             imported from ‘System.IO’
                             (and originally defined in ‘GHC.IO.Handle.FD’)

<interactive>:11:14: error:
    Ambiguous occurrence ‘stdout’
    It could refer to either ‘Turtle.stdout’,
                             imported from ‘Turtle’ at somefile.hs:12:1-13
                             (and originally defined in ‘Turtle.Prelude’)
                          or ‘System.IO.stdout’,
                             imported from ‘System.IO’
                             (and originally defined in ‘GHC.IO.Handle.FD’)

<interactive>:13:14: error:
    Ambiguous occurrence ‘stderr’
    It could refer to either ‘Turtle.stderr’,
                             imported from ‘Turtle’ at somefile.hs:12:1-13
                             (and originally defined in ‘Turtle.Prelude’)
                          or ‘System.IO.stderr’,
                             imported from ‘System.IO’
                             (and originally defined in ‘GHC.IO.Handle.FD’)
Examples: 0  Tried: 0  Errors: 0  Failures: 0
rx@mirabelle {master} ~/cfg/spin $

not sure how to best cope with that situation, using

{-# LANGUAGE NoImplicitPrelude #-}

causes me a lot of pain to import everything I need by hand

maybe I am doing something wrong? my turtle script runs just fine though,
it's just the fact that I cannot doctest it, that's annoying me

I can calm down the error msgs with

import Turtle hiding (stderr, stdout)

but really I would prefer Turtle's stderr/stdout over the ones from System.IO/Prelude
and thus stay in my Turtle world. however

import Prelude hiding (stderr, stdout)
import Turtle

does not help (I still get the errors above ?)

thanks

-Andreas

[Gabriella439]

Even if you do an open import for the Turtle package you can use Turtle.stderr in your doctest to disambiguate which stderr you meant

[reuleaux]

well thanks a lot. however the error messages are not coming from any particular usage of stdout/stderr in any doctests of my program, but from running doctest on an almost empty file already, consider this 3 lines program minimal.hs:

…

-------------------- module Foo where import Turtle -------------------- there is no doctest in there yet, and stdout isn't used either, nevertheless doctest complains (output truncated): rx@dell {master} ~/cfg/spin $ doctest -DDOCTEST minimal.hs <interactive>:5:14: error: Ambiguous occurrence ‘stdout’ It could refer to either ‘Turtle.stdout’, imported from ‘Turtle’ at minimal.hs:3:1-13 (and originally defined in ‘Turtle.Prelude’) or ‘System.IO.stdout’, imported from ‘System.IO’ (and originally defined in ‘GHC.IO.Handle.FD’) <interactive>:5:21: error: Ambiguous occurrence ‘stderr’ It could refer to either ‘Turtle.stderr’, imported from ‘Turtle’ at minimal.hs:3:1-13 (and originally defined in ‘Turtle.Prelude’) or ‘System.IO.stderr’, imported from ‘System.IO’ (and originally defined in ‘GHC.IO.Handle.FD’) these error messages are kind of distracting, so I calm them down with import Turtle hiding (stdout, stderr) import qualified Turtle as T and then I would later use eg. T.stdout in a silly function foo: foo :: (MonadIO io) => Shell Line -> io () foo = T.stdout that's the only way I have found to turn them off: import Turtle hiding (stdout, stderr) thus I cannot use, what would feel more natural, the style of open import import Turtle foo :: (MonadIO io) => Shell Line -> io () foo = stdout when I want to run doctest on my programs. I am aware that this is not a turtle bug, but rather a question: maybe the situation can be improved somehow ? it would be nice if my 3 lines / almost empty program above would not cause 6 error messages in doctest, and if I could use the simple pattern of open import import Turtle without hesitating usually. thanks again Gabriel Gonzalez <[email protected]> writes:

Even if you do an open import for the `Turtle` package you can use `Turtle.stderr` in your doctest to disambiguate which `stderr` you meant

[Gabriella439]

Oh, I see. I guess doctest is including some unqualified references to stderr and stdout in its own logic. If that is the case then your only resort is import Turtle hiding (stderr, stdout). I would also open up an issue against doctest to fully qualify its own stderr/stdout references since that seems like a bug to me

[reuleaux]

OK, will do. Gabriel Gonzalez <[email protected]> writes:

…

Oh, I see. I guess `doctest` is including some unqualified references to `stderr` and `stdout` in its own logic. If that is the case then your only resort is `import Turtle hiding (stderr, stdout)`. I would also open up an issue against `doctest` to fully qualify its own `stderr`/`stdout` references since that seems like a bug to me