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

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

[Jiří Wolker]

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

[John MacFarlane]

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
> 
> -- 
> You received this message because you are subscribed to the Google Groups "pandoc-discuss" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to pandoc-discuss+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
> To view this discussion on the web visit https://groups.google.com/d/msgid/pandoc-discuss/cada4d72-e81d-b39e-bd05-a6780b6848f5%40gmail.com.

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

[Jiří Wolker]

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Thanks for the fix. I had to recollect how to write programs in Haskell. 
I'll start new thread for the “P.S.” part of my original message.

Dne středa 27. července 2022 v 17:41:26 UTC+2 uživatel fiddlosopher napsal:

> 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 <wol...-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 
> > 
> > -- 
> > You received this message because you are subscribed to the Google 
> Groups "pandoc-discuss" group. 
> > To unsubscribe from this group and stop receiving emails from it, send 
> an email to pandoc-discus...-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org 
> > To view this discussion on the web visit 
> https://groups.google.com/d/msgid/pandoc-discuss/cada4d72-e81d-b39e-bd05-a6780b6848f5%40gmail.com. 
>
>
>

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