Copyright	(C) 2022-2023 Peter Lebbing
License	BSD2 (see the file LICENSE)
Maintainer	Peter Lebbing <peter@digitalbrains.com>
Safe Haskell	Safe-Inferred
Language	Haskell2010

Prettyprinter.Interpolate

Contents

Deprecated

Description

Efficient interpolation for Prettyprinter

This module provides efficient interpolation of string-interpolate quasi quoters when used with prettyprinters Documents.

The normal quasi quoters from string-interpolate do work when used as a Doc. Newlines are even converted to Prettyprinter.line. However, this method is inefficient. The following code functions correctly:

 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE QuasiQuotes #-}

 module Main where

 import Data.String.Interpolate
 import Data.Text (Text)
 import Prettyprinter

 f :: Text
 f = "world"

 g :: Doc ()
 g = [i|Hello #{f}!|]

 main :: IO ()
 main = print g

However, what happens under the hood is that f is converted to String, the interpolated string is built manipulating Strings, and then the output is converted to Text in prettyprinter. The following code is much better:

 g = pretty ([i|Hello #{f}!|] :: Text)

Now, the interpolated string is constructed as Text, and this is passed cleanly into Doc which also uses Text as its underlying type for representation of text. At no point is f converted to String, and the string construction benefits from the performance of Text. And again, newlines are converted to line.

This module defines wrapper quasi quoters that automatically perform the pretty invocation, and can simply be used as: