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Allegro CL version 8.1
Unrevised from 8.0 to 8.1. Minimal update since 8.1 release.
8.0 version

if*

Arguments: (test-form {then then-form+ | thenret} {elseif else-test-form {then else-then-form+ | thenret}}* [else else-form+])

This form consists of a series of clauses introduced by the symbols then, elseif, else, and thenret. First the predicate test-form is evaluated. If it is true, the then-forms are evaluated, and the value of the last such form is returned. If test-form evaluates to nil, any remaining clauses are processed. If no clauses remain, if* returns nil.

When a thenret clause is encountered no further evaluation takes place, and the value of the most recently evaluated test-form is returned.

When an elseif clause is encountered, the predicate else-test-form is evaluated. If it is true, the else-then-forms are evaluated, and the value of the last such form is returned; otherwise any remaining clauses are processed. If no clauses remain, if* returns nil. And lastly, when an else clause is encountered, the else-forms are evaluated, and the value of the last such form is returned.

Examples

;; The basic format of a IF* expression is:
;; 
;; (if* [test] then [do this 1] [do this 2] else [do other 1] [do other 2])
;;
;; When [test] is true, the forms after the THEN are evaluated and the
;; result of the last returned; if [test] if false, the forms after the
;; ELSE are evaluated and the result of the last is returned.

;; So:

cl-user(18): (if* (> 3 2) then "three is bigger" 3
                     else "three is smaller" 2)
3
;;  Your do not need an ELSE form:
cl-user(19): (if* (> 3 2) then "three is bigger" 3)
3
cl-user(19): (if* (> 2 3) then "two is bigger" 2)
nil

;; You can have multiple fors after THEN or ELSE:
cl-user(21): (defun foo (x) (if* x then (setq y 2) (print x) 
                                 else (setq y -2) "no"))
foo
cl-user(22): (foo 2)

2 
2
cl-user(23): (foo "hello")

"hello" 
"hello"
cl-user(24): (foo nil)
"no"
cl-user(25): 

;; There are two more special symbols: THENRET and ELSEIF.

;; THENRET says when the test is true just return the value of the test
;; form just evaluated:

cl-user(25): (if* (+ 4 5) thenret)
9
cl-user(26): 

;; ELSEIF introduces a new test, so you can have compound tests:

cl-user(27): (setq score 77)
77
cl-user(28): (if* (< score 60) then "F" 
                     elseif (< score 70) then "D"
		     elseif (< score 80) then "C" 
                     elseif (< score 90) then "B" 
                     else "A")
"C"
cl-user(29): (setq score 55)
55
cl-user(30): (if* (< score 60) then "F" 
                     elseif (< score 70) then "D"
		     elseif (< score 80) then "C" 
                     elseif (< score 90) then "B" 
                     else "A")
"F"
cl-user(31): (setq score 92)
92
cl-user(32): (if* (< score 60) then "F" 
                     elseif (< score 70) then "D"
		     elseif (< score 80) then "C" 
                     elseif (< score 90) then "B" 
                     else "A")
"A"
cl-user(33): 

Copyright (c) 1998-2009, Franz Inc. Oakland, CA., USA. All rights reserved.
Documentation for Allegro CL version 8.1. This page was not revised from the 8.0 page.
Created 2009.7.29.

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Allegro CL version 8.1
Unrevised from 8.0 to 8.1. Minimal update since 8.1 release.
8.0 version