Lisp - loop for construct

The loop for construct allows you to implement a for-loop like iteration as most common in other languages.

It allows you to

• set up variables for iteration

• specify expression(s) that will conditionally terminate the iteration

• specify expression(s) for performing some job on each iteration

• specify expression(s), and expressions for doing some job before exiting the loop

The for loop for construct follows several syntax −

(loop for loop-variable in <a list>
   do (action)
)

(loop for loop-variable from value1 to value2
   do (action)
)

Example - loop on strings

Create a new source code file named main.lisp and type the following code in it −

main.lisp

; loop on strings and print each value
(loop for x in '(tom dick harry)
   ; print x
   do (format t " ~s" x)
)

Output

When you click the Execute button, or type Ctrl+E, LISP executes it immediately and the result returned is −

TOM DICK HARRY

Example - loop on numbers

Update the source code file named main.lisp and type the following code in it −

main.lisp

; loop on each number and print
(loop for a from 10 to 20
   ; print a
   do (print a)
)

Output

When you click the Execute button, or type Ctrl+E, LISP executes it immediately and the result returned is −

10 
11 
12 
13 
14 
15 
16 
17 
18 
19 
20 

Example - conditional loop on numbers

Update the source code file named main.lisp and type the following code in it −

main.lisp

; loop numbers from 1 to 20
(loop for x from 1 to 20
   ; if number is even
   if(evenp x)
   ; print x
   do (print x)
)

Output

When you click the Execute button, or type Ctrl+E, LISP executes it immediately and the result returned is −

2 
4 
6 
8 
10 
12 
14 
16 
18 
20