Macro

Summary

Executes a body of code if a form evaluates to non- nil , propagating the result of the form through the body of code.

Package

lispworks

Signature

when-let ( var form ) &body body => result

Arguments

var

A variable whose value is used in the evaluation of body .

form

A form, which must evaluate to non- nil .

body

A body of code to be evaluated conditionally on the result of form .

Values

result

The result of evaluating body using the value var .

Description

This macro executes the body of code if the form evaluates to a non- nil result. Within the body, the variable var is bound to the result of the form .

Example

The form

(when-let (position (search string1 string2))

   (print position))

macroexpands to

(let ((position (search string1 string2)))

   (when position

      (print position)))