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- Lisp Macros
- LISP - Macros
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- LISP - Code Generation Using Macro
- LISP - Variable Capture and Hygienic macro
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- LISP - Macro Writing Style
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- Lisp Functions
- LISP - Functions
- LISP - Functions vs Macros
- LISP - Calling Function using funcall
- LISP - Calling Function using apply
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- LISP - Functions as Return Values
- LISP - Recursion
- LISP - Built-in Functions
- Lisp Predicates
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- LISP - Accessing Element of Sequence
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- LISP - Getting Subsequence
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- 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
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- LISP - Sorting a List
- LISP - Searching a List
- LISP - List vs Vectors
- LISP - Matrix Multiplication
- Lisp Vectors
- LISP - Vectors
- LISP - Creating Vectors
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- 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
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- LISP - Depth First Traversal
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- 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
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- Lisp - CLOS
- LISP - CLOS
- Lisp - Objects
- LISP - Class
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- LISP - Generic Functions
- LISP - Class Precedence
- LISP - Metaobject Protocol
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- 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 - when Construct
The when macro is followed by a test clause that evaluates to t or nil. If the test clause is evaluated to nil, then no form is evaluated and nil is returned, however the test result is t, then the action following the test clause is executed.
Syntax for when macro −
(when (test-clause) (<action1) )
Example
Create a new source code file named main.lisp and type the following code in it.
main.lisp
; set a as 100 (setq a 100) ; check if a is greater than 20 (when (> a 20) ; print the statement is above statement is true (format t "~% a is greater than 20")) ; print the statement (format t "~% value of a is ~d " a)
Output
When you click the Execute button, or type Ctrl+E, LISP executes it immediately and the result returned is −
a is greater than 20 value of a is 100
Example
Update file main.lisp and type the following code in it.
main.lisp
; set a as 10 (setq a 10) ; check if a is greater than 20 (when (> a 20) ; print the statement is above statement is true (format t "~% a is greater than 20")) ; print the statement (format t "~% value of a is ~d " a)
Output
When you click the Execute button, or type Ctrl+E, LISP executes it immediately and the result returned is −
value of a is 10
lisp_decisions.htm
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