
- LISP Tutorial
- LISP - Home
- LISP - Overview
- LISP - Environment
- LISP - REPL
- LISP - Program Structure
- LISP - Basic Syntax
- LISP - Data Types
- Lisp Macros
- LISP - Macros
- LISP - Backquote and Comma
- LISP - Code Generation Using Macro
- LISP - Variable Capture and Hygienic macro
- LISP - Scope and Binding
- LISP - Macro Writing Style
- LISP - Macro Characters
- LISP - Read-Time Macros
- LISP - Compiler Macros
- LISP - Uses of Macros
- Lisp Functions
- LISP - Functions
- LISP - Functions vs Macros
- LISP - Calling Function using funcall
- LISP - Calling Function using apply
- LISP - Closures
- LISP - Functions as Arguments
- LISP - Functions as Return Values
- LISP - Recursion
- LISP - Built-in Functions
- Lisp Predicates
- LISP - Predicates
- LISP - Generic Data Type Predicates
- LISP - Specific Data Type Predicates
- LISP - Equality Predicates
- LISP - Numeric Predicates
- LISP - Comparison Predicates
- LISP - Logical Predicates
- LISP - List Predicates
- LISP - Custom Predicates
- LISP - Chaining Predicates
- Lisp Arrays
- LISP - Arrays
- LISP - Adjustable Arrays
- LISP - Fill Pointers in Arrays
- LISP - Specialized Arrays
- LISP - Arrays Properties
- LISP - Iterating over Arrays
- LISP - Multidimensional Arrays
- LISP - Row-Major Order
- Lisp Strings
- LISP - Strings
- LISP - String Concatenation
- LISP - String Comparison
- LISP - String Case Conversion
- LISP - String Trimmimg
- LISP - String Searching
- LISP - Getting Substring
- LISP - String Replacement
- LISP - Sorting Strings
- LISP - Merging Strings
- LISP - Accessing Characters of String
- LISP - String length
- LISP - Escape Sequences
- Lisp Sequences
- LISP - Sequences
- LISP - Accessing Element of Sequence
- LISP - Sequence length
- LISP - Getting Subsequence
- LISP - Search Element in Sequence
- LISP - Sequence Concatenation
- LISP - Reversing a Sequence
- LISP - Mapping Sequence Element
- LISP - position of Element
- LISP - Remove an Element
- LISP - Sort Sequence
- LISP - Merge Sequences
- LISP - every function
- LISP - some function
- LISP - notany function
- LISP - notevery function
- Lisp Lists
- LISP - Lists
- LISP - Accessing Elements of Lists
- LISP - Modifications to Lists
- LISP - Using mapcar on List
- LISP - Using mapc on List
- LISP - Using reduce on List
- LISP - Removing elements from List
- LISP - Reversing a List
- LISP - Sorting a List
- LISP - Searching a List
- LISP - List vs Vectors
- LISP - Matrix Multiplication
- Lisp Vectors
- LISP - Vectors
- LISP - Creating Vectors
- LISP - Accessing Elements of Vectors
- LISP - Modifications to Vectors
- LISP - Adjustable Vectors
- LISP - Specialized Vectors
- LISP - Vector Functions
- Lisp Set
- LISP - Set
- LISP - Adding elements to the Set
- LISP - Getting SubSet from a Set
- LISP - Set Difference
- LISP - Set Exclusive OR
- LISP - Set Intersection
- LISP - Set Union
- LISP - Representing Set with HashTable
- LISP - List as Set vs HashTable as Set
- Lisp Tree
- LISP - Tree
- LISP - Recursive Traversal
- LISP - Inorder Traversal
- LISP - Preorder Traversal
- LISP - Postorder Traversal
- LISP - Depth First Traversal
- LISP - Modifying Tree
- LISP - Search Tree
- LISP - Binary Tree
- Lisp Hash Table
- LISP - Hash Table
- Adding Values to Hash Table
- Removing Values from Hash Table
- Updating Values of Hash Table
- Iterating Hash Table Entries
- Searching key in HashTable
- Checking Size of HashTable
- Using Custom Equality Check
- Lisp - Input − Output
- LISP - Input − Output
- LISP - Streams
- LISP - Reading Data from Streams
- LISP - Writing Data to Streams
- LISP - File I/O
- LISP - String I/O
- LISP - Formatting with Format
- LISP - Interactive I/O
- LISP - Error Handling
- LISP - Binary I/O
- Lisp - Structures
- LISP - Structures
- LISP - Accessors and Mutators
- LISP - Structure Options
- LISP - Structure Types
- LISP - Applications and Best Practices
- Lisp - CLOS
- LISP - CLOS
- Lisp - Objects
- LISP - Class
- LISP - Slots and Accessors
- LISP - Generic Functions
- LISP - Class Precedence
- LISP - Metaobject Protocol
- LISP - Multimethods
- LISP - Multiple Inheritance
- LISP - Method Combinations
- LISP - Method Combinations
- LISP - :before Method Combination
- LISP - :primary Method Combination
- LISP - :after Method Combination
- LISP - :around Method Combination
- LISP - + Method Combination
- LISP - and Method Combination
- LISP - append Method Combination
- LISP Useful Resources
- Lisp - Quick Guide
- Lisp - Useful Resources
- Lisp - Discussion
Lisp - Program Structure
LISP expressions are called symbolic expressions or s-expressions. The s-expressions are composed of three valid objects, atoms, lists and strings.
Any s-expression is a valid program.
LISP programs run either on an interpreter or as compiled code.
The interpreter checks the source code in a repeated loop, which is also called the read-evaluate-print loop (REPL). It reads the program code, evaluates it, and prints the values returned by the program.
A Simple Program
Let us write an s-expression to find the sum of three numbers 7, 9 and 11. To do this, we can type at the interpreter prompt.
; execuate sum of three numbers (+ 7 9 11)
LISP returns the result −
27
If you would like to run the same program as a compiled code, then create a LISP source code file named myprog.lisp and type the following code in it.
main.lisp
; print sum of three numbers (write (+ 7 9 11))
Output
When you click the Execute button, or type Ctrl+E, LISP executes it immediately and the result returned is −
27
LISP Uses Prefix Notation
You might have noted that LISP uses prefix notation.
In the above program the + symbol works as the function name for the process of summation of the numbers.
In prefix notation, operators are written before their operands. For example, the expression,
a * ( b + c ) / d
will be written as −
; prefix mode operation (/ (* a (+ b c) ) d)
Let us take another example, let us write code for converting Fahrenheit temp of 60o F to the centigrade scale −
The mathematical expression for this conversion will be −
(60 * 9 / 5) + 32
Create a source code file named main.lisp and type the following code in it.
main.lisp
; evaluate and print arithmetic expression (write(+ (* (/ 9 5) 60) 32))
Output
When you click the Execute button, or type Ctrl+E, LISP executes it immediately and the result returned is−
140
Evaluation of LISP Programs
Evaluation of LISP programs has two parts −
Translation of program text into Lisp objects by a reader program
Implementation of the semantics of the language in terms of these objects by an evaluator program
The evaluation process takes the following steps −
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 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.
The 'Hello World' Program
Learning a new programming language doesn't really take off until you learn how to greet the entire world in that language, right!
So, please create new source code file named main.lisp and type the following code in it.
main.lisp
; print Hello World (write-line "Hello World") ; print the statement (write-line "I am at 'Tutorials Point'! Learning LISP")
Output
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