Writing a filter to add current date to document's metadata

Writing a filter to add current date to document's metadata

[Jason White]

I'm interested in writing a filter to add the current date to the document's
metadata before writing the output. I suspect it can be accomplished in
several well constructed lines of Haskell, but I'm having difficulty working
out what to specify as the pattern matching expression in writing a JSON
filter.

Any hints? I'm still very much a Haskell beginner.

Re: Writing a filter to add current date to document's metadata

[John MacFarlane]

Try something like this:

import Text.Pandoc.JSON
import Text.Pandoc.Builder (setMeta, text)

main = toJSONFilter addDate

addDate :: Pandoc -> IO Pandoc
addDate doc = do
  today <- return "TODAYS DATE" -- something from time
  return $ setMeta "date" (text today) doc

Re: Writing a filter to add current date to document's metadata

[Jason White]

John MacFarlane <jgm-TVLZxgkOlNX2fBVCVOL8/A@public.gmane.org> wrote:
> Try something like this:

[...]

Thank you. This is much appreciated.

As an aside, someone should conduct a survey of philosophers' programming
language preferences. It would be interesting to know whether there's a
stronger than average inclination toward logic and functional programming.

Re: Writing a filter to add current date to document's metadata

[Jason White]

John MacFarlane <jgm-TVLZxgkOlNX2fBVCVOL8/A@public.gmane.org> wrote:
> Try something like this:
> 
> import Text.Pandoc.JSON
> import Text.Pandoc.Builder (setMeta, text)
> 
> main = toJSONFilter addDate
> 
> addDate :: Pandoc -> IO Pandoc
> addDate doc = do
>  today <- return "TODAYS DATE" -- something from time
>  return $ setMeta "date" (text today) doc

I completed your above outline as follows. May I distribute this as part of a
project, under liberal licensing terms?

Anyone else is free to use, modify or redistribute  this for any purpose so
far as I'm concerned.


#!/usr/bin/env runhaskell
-- Insert today's date into a document's metadata.
-- Portions copyright (C) 2015 by John MacFarlane.
import Text.Pandoc.JSON (Pandoc, toJSONFilter)
import Text.Pandoc.Builder (setMeta, text)
import Data.Time.LocalTime (getZonedTime)
import Data.Time.Format (formatTime)
import System.Locale (defaultTimeLocale)

main = toJSONFilter addDate where
  addDate :: Pandoc -> IO Pandoc
  addDate doc = do
    localTime <- getZonedTime
    let today = formatTime defaultTimeLocale "%-d %B %Y" localTime in
     return $ setMeta "date" (text today) doc

Re: Writing a filter to add current date to document's metadata

[John MacFarlane]

+++ Jason White [Mar 22 15 10:35 ]:
>John MacFarlane <jgm-TVLZxgkOlNX2fBVCVOL8/A@public.gmane.org> wrote:
>> Try something like this:
>>
>> import Text.Pandoc.JSON
>> import Text.Pandoc.Builder (setMeta, text)
>>
>> main = toJSONFilter addDate
>>
>> addDate :: Pandoc -> IO Pandoc
>> addDate doc = do
>>  today <- return "TODAYS DATE" -- something from time
>>  return $ setMeta "date" (text today) doc
>
>I completed your above outline as follows. May I distribute this as part of a
>project, under liberal licensing terms?

Sure.