Re: [Maybe bug in docs] Filter “includes.hs” does not work for me

[John MacFarlane <fiddlosopher-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

You're right.  I will fix that in the documentation (though it won't update on the website til the next release).  Thank you.



> On Jul 27, 2022, at 5:14 AM, Jiří Wolker <woljiri-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> 
> Hello everyone,
> 
> I've probably found a bug in filter example that can be found in the docs (https://pandoc.org/filters.html#include-files). The original source code is:
> 
>    #!/usr/bin/env runhaskell
>    -- includes.hs
>    import Text.Pandoc.JSON
>    import qualified Data.Text.IO as TIO
>    import qualified Data.Text as T
> 
>    doInclude :: Block -> IO Block
>    doInclude cb@(CodeBlock (id, classes, namevals) contents) =
>      case lookup "include" namevals of
>           Just f     -> CodeBlock (id, classes, namevals) <$>
>                          TIO.readFile (T.unpack f)
>           Nothing    -> return cb
>    doInclude x = return x
> 
>    main :: IO ()
>    main = toJSONFilter doInclude
> 
> When I tried to execute it, it fails:
> 
>    …/include.hs:12:25: error:
>        * Couldn't match type `T.Text' with `[Char]'
>          Expected: [(String, T.Text)]
>            Actual: [(T.Text, T.Text)]
>        * In the second argument of `lookup', namely `namevals'
>          In the expression: lookup "include" namevals
>          In the expression:
>            case lookup "include" namevals of
>              Just f
>                -> CodeBlock (id, classes, namevals) <$> TIO.readFile (T.unpack f)
>              Nothing -> return cb
>       |
>    12 |   case lookup "include" namevals of
>       |                         ^^^^^^^^
>    Error running filter …/filters/include.hs:
>    Filter returned error status 1
> 
> To fix the filter, I had to change the line with “case” to this:
> 
>      case lookup (T.pack "include") namevals of
> 
> (i.e. call T.pack on the string literal.)
> 
> I am quite new to Haskell, correct me if I am wrong.
> 
> It is possible that this is dependent on the version of Haskell. I use runghc 9.0.2 to run the script.
> 
> P.S.:  It would be nice to include few scripts in the Pandoc distribution. Ideas: includes.hs, directory listing (I write a div with special class and it produces directory listing in the text.) I will probably write the listing filter soon. It could be nice for creating directory “overview”/readme files.
> 
> 
> Thanks.
> Jiří
> 
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