base-4.3.1.0: Basic libraries

Portabilityportable
Stabilityprovisional
Maintainer[email protected]

Text.Printf

Description

A C printf like formatter.

Synopsis

Documentation

printf :: PrintfType r => String -> rSource

Format a variable number of arguments with the C-style formatting string. The return value is either String or (IO a).

The format string consists of ordinary characters and /conversion specifications/, which specify how to format one of the arguments to printf in the output string. A conversion specification begins with the character %, followed by one or more of the following flags:

    -      left adjust (default is right adjust)
    +      always use a sign (+ or -) for signed conversions
    0      pad with zeroes rather than spaces

followed optionally by a field width:

    num    field width
    *      as num, but taken from argument list

followed optionally by a precision:

    .num   precision (number of decimal places)

and finally, a format character:

    c      character               Char, Int, Integer, ...
    d      decimal                 Char, Int, Integer, ...
    o      octal                   Char, Int, Integer, ...
    x      hexadecimal             Char, Int, Integer, ...
    X      hexadecimal             Char, Int, Integer, ...
    u      unsigned decimal        Char, Int, Integer, ...
    f      floating point          Float, Double
    g      general format float    Float, Double
    G      general format float    Float, Double
    e      exponent format float   Float, Double
    E      exponent format float   Float, Double
    s      string                  String

Mismatch between the argument types and the format string will cause an exception to be thrown at runtime.

Examples:

   > printf "%d\n" (23::Int)
   23
   > printf "%s %s\n" "Hello" "World"
   Hello World
   > printf "%.2f\n" pi
   3.14

hPrintf :: HPrintfType r => Handle -> String -> rSource

Similar to printf, except that output is via the specified Handle. The return type is restricted to (IO a).

class PrintfType t Source

The PrintfType class provides the variable argument magic for printf. Its implementation is intentionally not visible from this module. If you attempt to pass an argument of a type which is not an instance of this class to printf or hPrintf, then the compiler will report it as a missing instance of PrintfArg.

Instances

IsChar c => PrintfType [c] 
PrintfType (IO a) 
(PrintfArg a, PrintfType r) => PrintfType (a -> r) 

class HPrintfType t Source

The HPrintfType class provides the variable argument magic for hPrintf. Its implementation is intentionally not visible from this module.

Instances

HPrintfType (IO a) 
(PrintfArg a, HPrintfType r) => HPrintfType (a -> r) 

class IsChar c Source

Instances