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