Well-typed, flexible and variadic printf for Haskell.

More type-safe, flexible replacement of variadic printf for Text.Printf.

safe-printf -- Well-typed, variadic and flexible printf functions for Haskell

What is this?

Haskell's standard Text.Printf module provides variadic printf function but not type-safe. This library provides an alternative for this, more type-safe version of printf function, combinators and quasiquoters.

The current implementation is just a proof-of-concept, so it is not so efficient and provides APIs only for String value generation. In future, we will support Text types and improve the effiiciency.

Install

$ git clone https://github.com/konn/safe-printf.git
$ cd safe-printf
$ cabal install

Usage

We provide two interfaces to construct format: smart constructors and quasiquoters.

Smart constructors

You need OverloadedStrings extension.

{-# LANGUAGE OverloadedStrings #-}
module Main where
import Text.Printf.Safe             (printf, (%), (><))
import Text.Printf.Safe.Combinators (b', d, _S)
main = do
  putStrLn $ printf ("1 + 2 = " %d >< " and 0 == 1 is " %_S >< "." ) (1 + 2) (0 == 1)
  putStrLn $ printf ("42 is " % b' '0' 10 >< "in binary.") 42
  putStrLn $ printf ("48% of people answers that the negation of True is" %(show . not) >< ".") True

Quasiquote interface

Quiasiquote interface provides more readable way for generating formats.

{-# LANGUAGE QuasiQuotes #-}
module Main where
import Text.Printf.Safe    (printf, fmt)
main = do
  putStrLn $ printf [fmt|1 + 2 = %d and 0 == 1 is %S.|] (1 + 2) (0 == 1)
  putStrLn $ printf [fmt|42 is %010b in binary.|] 42
  putStrLn $ printf [fmt|48%% of people answers that the negation of True is %{show . not}.|] True

TODO

• Support Text and perhaps Builder.
• Improve efficiency.
• Provide IO functions?

Licence

BSD3

Copyright

(c) Hiromi ISHII 2015