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- Lisp Functions
- LISP - Functions
- LISP - Functions vs Macros
- LISP - Calling Function using funcall
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- LISP - Remove an Element
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- 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
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- LISP - List vs Vectors
- LISP - Matrix Multiplication
- Lisp Vectors
- LISP - Vectors
- LISP - Creating Vectors
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- Lisp Set
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- LISP - Adding elements to the Set
- LISP - Getting SubSet from a Set
- LISP - Set Difference
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- LISP - Representing Set with HashTable
- LISP - List as Set vs HashTable as Set
- Lisp Tree
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- 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
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- Lisp - CLOS
- LISP - CLOS
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- 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 - Constants
In LISP, constants are variables that never change their values during program execution. Constants are declared using the defconstant construct.
Syntax
The defun construct is used for defining a function, we will look into it in the Functions chapter.
(defconstant PI 3.141592)
Example - Create Constant
The following example shows declaring a global constant PI and later using this value inside a function named area-circle that calculates the area of a circle.
Create a new source code file named main.lisp and type the following code in it.
main.lisp
; define a constant PI as 3.141592 (defconstant PI 3.141592) ; define a function area-circle (defun area-circle(rad) ; terminate current printing (terpri) ; print the redius (format t "Radius: ~5f" rad) ; print the area (format t "~%Area: ~10f" (* PI rad rad))) ; call the area-cirlce function with argument as 10 (area-circle 10)
Output
When you click the Execute button, or type Ctrl+E, LISP executes it immediately and the result returned is.
Radius: 10.0 Area: 314.1592
We can check if a constant is defined or not using boundp construct.
Syntax
; returns T if constant is available else return Nil (boundp 'PI)
Example - Check Constant if Exists
The following example shows declaring a global constant PI and later using boundp construct, we're checking existence of PI and in next statement, we're checking another undefined constant.
Create a new source code file named main.lisp and type the following code in it.
main.lisp
; define a constant PI as 3.141592 (defconstant PI 3.141592) ; check if PI constant is defined (write (boundp 'PI)) ; prints T ; terminate printing (terpri) ; check if OMEGA constant is defined (write (boundp 'OMEGA)) ; prints Nil
Output
When you click the Execute button, or type Ctrl+E, LISP executes it immediately and the result returned is.
T NIL