Text.Shakespeare.Text does not work well with superscripts in LaTeX text

[braunwolfgang]

I am using shakespeare to render LaTeX code with template files. I found that shakespeare creates compile errors when superscripts in LaTeX are used. I guess that the reason is based on the ^{ syntax from the html/css shakespeare part.

I dont know if this is intended or a bug of the parser.

A minimal example (stack lts-10.7) is given in the code fragment below.

#!/usr/bin/env stack
-- stack --resolver lts-10.7 script --package shakespeare --package text

{-# LANGUAGE QuasiQuotes #-}

module Main where

import Text.Shakespeare.Text

import qualified Data.Text.Lazy as TL
import qualified Data.Text.Lazy.IO as TLIO

{-
Using text for LaTeX import can be difficult:

foo provides the text in "tex file" 2^23
but pdflatex will render it with 2 in superscript and 3 in normal font
-}
foo :: TL.Text
foo = [lt|2^#{bar}|]
  where bar = 23 :: Int

{-
To fix this the superscript has to be enclosed in { .. }, however this results
in compile errors:

shakespeare-caret-bug.hs:18:8: error:
    • Exception when trying to run compile-time code:
        "2^{#{foo}}" (line 1, column 4):
unexpected "#"
expecting "[", "(", "-", digit, "\"", uppercase letter, letter or digit, "_" or "'"
CallStack (from HasCallStack):
  error, called at ./Text/Shakespeare.hs:202:23 in shakespeare-2.0.15-HbvJ7t5PaRN2XZniCryTrC:Text.Shakespeare
      Code: template-haskell-2.12.0.0:Language.Haskell.TH.Quote.quoteExp
              lt "2^{#{foo}}"
    • In the quasi-quotation: [lt|2^{#{foo}}|]
   |
18 | foo2 = [lt|2^{#{foo}}|]
   |        ^^^^^^^^^^^^^^^^

-}

foo2 :: TL.Text
foo2 = [lt|2^{#{bar}}|]
  where bar = 23 :: Int

{-

A workaround can be achieved using ^\{, but this is not documented in

https://www.yesodweb.com/book/shakespearean-templates

or in the haddock

http://hackage.haskell.org/package/shakespeare-2.0.15/docs/Text-Shakespeare-Text.html

-}
foo3 :: TL.Text
foo3 = [lt|2^\{#{bar}}|]
  where bar = 23 :: Int

main :: IO ()
main = do
  TLIO.putStrLn foo
  TLIO.putStrLn foo2
  TLIO.putStrLn foo3

[snoyberg]

This is intentional, we treat the parsing the same way. If you can send a PR update for the docs to clarify the necessity of escaping, that would be great.