base-4.2.0.0: Basic librariesContentsIndex
Text.Printf
Portabilityportable
Stabilityprovisional
Maintainerlennart@augustsson.net
Description
A C printf like formatter.
Synopsis
printf :: PrintfType r => String -> r
hPrintf :: HPrintfType r => Handle -> String -> r
class PrintfType t
class HPrintfType t
class PrintfArg a
class IsChar c
Documentation
printf :: PrintfType r => String -> r

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 -> r
Similar to printf, except that output is via the specified Handle. The return type is restricted to (IO a).
class PrintfType t
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.
class HPrintfType t
The HPrintfType class provides the variable argument magic for hPrintf. Its implementation is intentionally not visible from this module.
class PrintfArg a
class IsChar c
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