LISP - Basic Syntax

LISP programs are made up of three basic building blocks −
atom
atom
list
list
string
string
An atom is a number or string of contiguous characters. It includes numbers and special characters.
Following are examples of some valid atoms −
hello-from-tutorials-point
name
123008907
*hello*
Block#221
abc123
A list is a sequence of atoms and/or other lists enclosed in parentheses.
Following are examples of some valid lists −
( i am a list)
(a ( a b c) d e fgh)
(father tom ( susan bill joe))
(sun mon tue wed thur fri sat)
( )
A string is a group of characters enclosed in double quotation marks.
Following are examples of some valid strings −
" I am a string"
"a ba c d efg #$%^&!"
"Please enter the following details :"
"Hello from 'Tutorials Point'! "
The semicolon symbol (;) is used for indicating a comment line.
For Example,
(write-line "Hello World") ; greet the world

; tell them your whereabouts

(write-line "I am at 'Tutorials Point'! Learning LISP")
When you click the Execute button, or type Ctrl+E, LISP executes it immediately and the result returned is −
Hello World

I am at 'Tutorials Point'! Learning LISP

Following are some of the important points to note −
The basic numeric operations in LISP are +, -, *, and /
The basic numeric operations in LISP are +, -, *, and /
LISP represents a function call f(x) as (f x), for example cos(45) is written as cos 45
LISP represents a function call f(x) as (f x), for example cos(45) is written as cos 45
LISP expressions are case-insensitive, cos 45 or COS 45 are same.
LISP expressions are case-insensitive, cos 45 or COS 45 are same.
LISP tries to evaluate everything, including the arguments of a function. Only three types of elements are constants and always return their own value

Numbers
The letter t, that stands for logical true.
The value nil, that stands for logical false, as well as an empty list.


LISP tries to evaluate everything, including the arguments of a function. Only three types of elements are constants and always return their own value
Numbers
Numbers
The letter t, that stands for logical true.
The letter t, that stands for logical true.
The value nil, that stands for logical false, as well as an empty list.
The value nil, that stands for logical false, as well as an empty list.
In the previous chapter, we mentioned that the evaluation process of LISP code takes the following steps.
The reader translates the strings of characters to LISP objects or s-expressions.
The reader translates the strings of characters to LISP objects or s-expressions.
The evaluator defines syntax of Lisp forms that are built from s-expressions. This second level of evaluation defines a syntax that determines which s-expressions are LISP forms.
The evaluator defines syntax of Lisp forms that are built from s-expressions. This second level of evaluation defines a syntax that determines which s-expressions are LISP forms.
Now, a LISP forms could be.
An Atom
An Atom
An empty or non-list
An empty or non-list
Any list that has a symbol as its first element
Any list that has a symbol as its first element
The evaluator works as a function that takes a valid LISP form as an argument and returns a value. This is the reason why we put the LISP expression in parenthesis, because we are sending the entire expression/form to the evaluator as arguments.
Name or symbols can consist of any number of alphanumeric characters other than whitespace, open and closing parentheses, double and single quotes, backslash, comma, colon, semicolon and vertical bar. To use these characters in a name, you need to use escape character (\).
A name can have digits but not entirely made of digits, because then it would be read as a number. Similarly a name can have periods, but can't be made entirely of periods.
LISP evaluates everything including the function arguments and list members.
At times, we need to take atoms or lists literally and don't want them evaluated or treated as function calls.
To do this, we need to precede the atom or the list with a single quotation mark.
The following example demonstrates this.
Create a file named main.lisp and type the following code into it.
(write-line "single quote used, it inhibits evaluation")
(write '(* 2 3))
(write-line " ")
(write-line "single quote not used, so expression evaluated")
(write (* 2 3))
When you click the Execute button, or type Ctrl+E, LISP executes it immediately and the result returned is −
single quote used, it inhibits evaluation
(* 2 3) 
single quote not used, so expression evaluated
6


    79 Lectures 
     7 hours 

 Arnold Higuit
 Print
 Add Notes
 Bookmark this page