12 The LISPWORKS Package

when-let

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)))