Data.String.Interpolation

This module defines a quasiquoter for interpolated strings. For example:

  import qualified Data.Text.Lazy as LT
  let fb x | x `mod` 15 == 0 = "FizzBuzz" 
           | x `mod` 5 == 0 = "Buzz" 
           | x `mod` 3 == 0 = "Fizz" 
           | otherwise = LT.pack (show x)

>>> LT.take 85 [str|#x in [1..]:$fb x$|, #|] <> ".. "
"1, 2, Fizz, 4, Buzz, Fizz, 7, 8, Fizz, Buzz, 11, Fizz, 13, 14, FizzBuzz, 16, 17, Fizz.. "

Documentation

str :: QuasiQuoter

Quasiquote str implements multiline strings with interpolation. Interpolating a value into the string is done by $<String expression>$ and interpolating anything with instance Show is $:<Show expression>$. Due to pretty deep limitations, the parser is not able to properly deduce associtivity of infix operators, so use lots and lots of parenthesis.

Repetitive patterns can be made with # symbol:

  #<pattern> in <list>: <interpolated string> (|<interpolated string>)#

Where (|<interpolated string>) denotes optional separator for the elements.

Multiline indentation is handled by aligning on smallest un-empty line after the first. Neither pattern matching nor nested #-patterns are supported, however, see example below.

Normal '\\n' style escaping of special characters is intentionally not supported. Please use $endline$ or $n$ style instead.

As an example, let's plot set of vectors with gnuplot:

   plotVecs :: [(String,[Double])] -> String
   plotVecs vs =  
       [$str| ## Plot multiple vectors
              plot #(n,_) in vs:- with lines lw 5 title $:n$ |, #
              #d in map snd vs:$singleVec d$$endline$e$endline$# |]
   where
    singleVec n = [$str|#(e,i) in zip n [1..]: $:i$ $:e$|$endline$#|]

  *Gnuplotter> plotVecs [("A",[1..5]),("B",[2..6])]
  # Plot multiple vectors
   plot - with lines lw 5 title "A" , - with lines lw 5 title "B" 
    1 1.0
    2 2.0
    3 3.0
    4 4.0
    5 5.0

e
    1 2.0
    2 3.0
    3 4.0
    4 5.0
    5 6.0

e

prnt :: QuasiQuoter

endline :: IsString a => a

End of the line

tab :: IsString a => a

Tab