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Allegro CL version 8.2
Unrevised from 8.1 to 8.2.
8.1 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) 1998-2016, Franz Inc. Oakland, CA., USA. All rights reserved.
This page was not revised from the 8.1 page.
Created 2010.1.21.

ToCDocOverviewCGDocRelNotesFAQIndexPermutedIndex
Allegro CL version 8.2
Unrevised from 8.1 to 8.2.
8.1 version