Format (Common Lisp)

In the Common Lisp programming language, format produces formatted output by outputting the characters of control-string and observing that a tilde introduces a directive. The character after the tilde, possibly preceded by prefix parameters and modifiers, specifies what kind of formatting is desired. Most directives use one or more elements of args to create their output.

If destination is a string, a stream, or t, then the result is nil. Otherwise, the result is a string containing the `output.'

format is useful for producing nicely formatted text, producing good-looking messages, and so on. format can generate and return a string or output to destination.

Syntax

format destination control-string &rest args ⇒ result

Arguments and Values

destination 

nil, t, a stream, or a string with a fill pointer.

control-string: a format control.

args 

format arguments for control-string.

result 

if destination is non-nil, then nil; otherwise, a string.

Exceptional Situations

If destination is a string with a fill pointer, the consequences are undefined if destructive modifications are performed directly on the string during the dynamic extent of the call.