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Functional Programming
                       with

    LISt Processing


   © 2010 Anil Kumar Pugalia <email@sarika-pugs.com>
                  All Rights Reserved.
Introduction




© 2010 Anil Kumar Pugalia <email@sarika-pugs.com>
               All Rights Reserved.
What to Expect?
W's of LISP
Language Specifics
Fun with Recursion




          © 2010 Anil Kumar Pugalia <email@sarika-pugs.com>   3
                         All Rights Reserved.
What is LISP?
Functional Programming Language
  Conceived by John McCarthy in 1956
Name comes from its initial powerful List Processing features
Natural computation mechanism: Recursion
Standardization as Common LISP
  ANSI released standards in 1996
Thought of as for Artificial Intelligence
  But could pretty much do anything
Examples range from OS, editors, compilers, games, GUIs, and
you think of it
                 © 2010 Anil Kumar Pugalia <email@sarika-pugs.com>   4
                                All Rights Reserved.
Current Available Forms
ANSI Common Lisp: clisp
  Compiler, Interpreter, Debugger
GNU Common Lisp: gcl
  Compiler, Interpreter
CMU Common Lisp: cmucl
  By Carnegie Mellon University
  Default available as .deb packages
  Use “alien –to-rpm" to convert them to rpm
Allegro CL: Commercial Common Lisp implementation
               © 2010 Anil Kumar Pugalia <email@sarika-pugs.com>   5
                              All Rights Reserved.
Why LISP?
“The programmable programming language"
What's good for the language's designer
  Is good for the language's users
Wish for new features for easier programming?
  As you can just add the feature yourself
Code the way our brain thinks: Recursive
  Most natural way of programming
50 lines of Code
             © 2010 Anil Kumar Pugalia <email@sarika-pugs.com>   6
                            All Rights Reserved.
Language Specifics
Data Structures
Basic Operations
Control Structures
Basic I/O




             © 2010 Anil Kumar Pugalia <email@sarika-pugs.com>   7
                            All Rights Reserved.
Data Structures
S-Expression: Atom or List
Atom: String of characters ('Values or Variables)
  Peace, 95432, -rtx, etc
List: Collection of S-Expressions enclosed by ()
  (The 100 times done)
  (Guava (43 (2.718 5) 56) Apple)
What is a Null List: ()?
Common Pitfall: Lists need to start with '
             © 2010 Anil Kumar Pugalia <email@sarika-pugs.com>   8
                            All Rights Reserved.
Basic Operations
Lisp Program = Sequence of Functions
  Applied to their Arguments
  Returning Lisp Objects
Function Types
  Predicate
    Tests conditions with its arguments
    Returns Nil (FALSE) or anything else (TRUE)
  Command
    Performs operation with its arguments
    Returns an S-Expression
                © 2010 Anil Kumar Pugalia <email@sarika-pugs.com>   9
                               All Rights Reserved.
Basic Operations ...
Format: (function arg1 arg2 … argn)
Let's try
  Commands: car, cdr, cons, quote
  Predicates: atom, null
NB Lisp is case-insensitive
More: first, last, rest, append, consp, ...


             © 2010 Anil Kumar Pugalia <email@sarika-pugs.com>   10
                            All Rights Reserved.
Mathematical Operations
Predicates: zerop, plusp, evenp, integerp, floatp
Arithmetic: +, -, *, /, rem, 1+, 1-
Comparisons: =, /=, <, >, <=, >=
Rounding: floor, ceiling, truncate, round
More Functions
  max, min, exp, expt, log, abs, signum, sqrt, isqrt


             © 2010 Anil Kumar Pugalia <email@sarika-pugs.com>   11
                            All Rights Reserved.
Control Structures
Constants & Variables: Atoms w/ & w/o quote (')
Assignment: setq, psetq, set, setf
Conditionals: equal, cond, if
Logical: and, or, not
Functions
  (defun func-name (par1 … parn) (commands))
  Unnamed: (lambda (par1 … parn) (commands))

            © 2010 Anil Kumar Pugalia <email@sarika-pugs.com>   12
                           All Rights Reserved.
Let's try some functions
Extract the second element from a list
Insert an element at second position in a list
Change nth element in a list
Find length of a list (iteratively)
Find variance of a list of elements




             © 2010 Anil Kumar Pugalia <email@sarika-pugs.com>   13
                            All Rights Reserved.
Iteration is Human
     Recursion is God




© 2010 Anil Kumar Pugalia <email@sarika-pugs.com>   14
               All Rights Reserved.
Recursion
 For any recursion, we need 2 things
     Recursive Relation
     Termination Condition
                         Functional                Procedural

Recursive Relation   From Mathematics.       Tricky Extreme
                     Fairly Simple           Conditions

Termination          Needs Thought           Fairly Trivial
Condition



 Let's try some examples to understand
                     © 2010 Anil Kumar Pugalia <email@sarika-pugs.com>   15
                                    All Rights Reserved.
Tracing & Analysis
Tracing Recursive Function Calls
  Enable tracing: (trace recursive-func)
  Invoke the function to be traced: (recursive-func …)
Performance Analysis
  (time (func …))
  Samples with our recursive functions



            © 2010 Anil Kumar Pugalia <email@sarika-pugs.com>   16
                           All Rights Reserved.
Tail Recursion
Bottom most call's return = Topmost call's return
  Let's observe the trace on list reversal
May not be always possible
But if possible, it is a smart compiler advantage
  Cuts-off processing as soon as lowest level returns




             © 2010 Anil Kumar Pugalia <email@sarika-pugs.com>   17
                            All Rights Reserved.
Example: Set Operations
Sets: List of AToms (LATs)
Operations: member, union, intersection, adjoin
Let's write some examples
  which support sets being elements of set




            © 2010 Anil Kumar Pugalia <email@sarika-pugs.com>   18
                           All Rights Reserved.
Basic Input / Output
Basic Input
  (read [input-stream] [eof-error] [eof-value]) → s-expr
Basic Output
  (print s-expr [output-stream]) → s-expr
  (format destination control-string [args])




              © 2010 Anil Kumar Pugalia <email@sarika-pugs.com>   19
                             All Rights Reserved.
Loading Files
Loading Lisp file for interpretation
  (load "file.lisp")
Compiling a Lisp file
  (compile "file.lisp") or (compile "file")
Loading a compiled Lisp file
  (load (compile "file.lisp"))



              © 2010 Anil Kumar Pugalia <email@sarika-pugs.com>   20
                             All Rights Reserved.
References
Common Lisp: http://www.lisp.org
CLISP: http://clisp.cons.org
Practical Common Lisp by Peter Seibel
  Also @ http://www.gigamonkeys.com/book/
LISP Tutorial: http://www.mars.cs.unp.ac.za/lisp/




           © 2010 Anil Kumar Pugalia <email@sarika-pugs.com>   21
                          All Rights Reserved.
What all have we learnt?
W's of LISP
Language Specifics Demonstration
  Data Structures
  Basic Operations
  Control Structures
  Basic I/O
Fun with Recursion
  Power, Tail Recursion, Tracing & Analysis
              © 2010 Anil Kumar Pugalia <email@sarika-pugs.com>   22
                             All Rights Reserved.
Any Queries?




© 2010 Anil Kumar Pugalia <email@sarika-pugs.com>   23
               All Rights Reserved.

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Functional Programming with LISP

  • 1. Functional Programming with LISt Processing © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> All Rights Reserved.
  • 2. Introduction © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> All Rights Reserved.
  • 3. What to Expect? W's of LISP Language Specifics Fun with Recursion © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 3 All Rights Reserved.
  • 4. What is LISP? Functional Programming Language Conceived by John McCarthy in 1956 Name comes from its initial powerful List Processing features Natural computation mechanism: Recursion Standardization as Common LISP ANSI released standards in 1996 Thought of as for Artificial Intelligence But could pretty much do anything Examples range from OS, editors, compilers, games, GUIs, and you think of it © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 4 All Rights Reserved.
  • 5. Current Available Forms ANSI Common Lisp: clisp Compiler, Interpreter, Debugger GNU Common Lisp: gcl Compiler, Interpreter CMU Common Lisp: cmucl By Carnegie Mellon University Default available as .deb packages Use “alien –to-rpm" to convert them to rpm Allegro CL: Commercial Common Lisp implementation © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 5 All Rights Reserved.
  • 6. Why LISP? “The programmable programming language" What's good for the language's designer Is good for the language's users Wish for new features for easier programming? As you can just add the feature yourself Code the way our brain thinks: Recursive Most natural way of programming 50 lines of Code © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 6 All Rights Reserved.
  • 7. Language Specifics Data Structures Basic Operations Control Structures Basic I/O © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 7 All Rights Reserved.
  • 8. Data Structures S-Expression: Atom or List Atom: String of characters ('Values or Variables) Peace, 95432, -rtx, etc List: Collection of S-Expressions enclosed by () (The 100 times done) (Guava (43 (2.718 5) 56) Apple) What is a Null List: ()? Common Pitfall: Lists need to start with ' © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 8 All Rights Reserved.
  • 9. Basic Operations Lisp Program = Sequence of Functions Applied to their Arguments Returning Lisp Objects Function Types Predicate Tests conditions with its arguments Returns Nil (FALSE) or anything else (TRUE) Command Performs operation with its arguments Returns an S-Expression © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 9 All Rights Reserved.
  • 10. Basic Operations ... Format: (function arg1 arg2 … argn) Let's try Commands: car, cdr, cons, quote Predicates: atom, null NB Lisp is case-insensitive More: first, last, rest, append, consp, ... © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 10 All Rights Reserved.
  • 11. Mathematical Operations Predicates: zerop, plusp, evenp, integerp, floatp Arithmetic: +, -, *, /, rem, 1+, 1- Comparisons: =, /=, <, >, <=, >= Rounding: floor, ceiling, truncate, round More Functions max, min, exp, expt, log, abs, signum, sqrt, isqrt © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 11 All Rights Reserved.
  • 12. Control Structures Constants & Variables: Atoms w/ & w/o quote (') Assignment: setq, psetq, set, setf Conditionals: equal, cond, if Logical: and, or, not Functions (defun func-name (par1 … parn) (commands)) Unnamed: (lambda (par1 … parn) (commands)) © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 12 All Rights Reserved.
  • 13. Let's try some functions Extract the second element from a list Insert an element at second position in a list Change nth element in a list Find length of a list (iteratively) Find variance of a list of elements © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 13 All Rights Reserved.
  • 14. Iteration is Human Recursion is God © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 14 All Rights Reserved.
  • 15. Recursion For any recursion, we need 2 things Recursive Relation Termination Condition Functional Procedural Recursive Relation From Mathematics. Tricky Extreme Fairly Simple Conditions Termination Needs Thought Fairly Trivial Condition Let's try some examples to understand © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 15 All Rights Reserved.
  • 16. Tracing & Analysis Tracing Recursive Function Calls Enable tracing: (trace recursive-func) Invoke the function to be traced: (recursive-func …) Performance Analysis (time (func …)) Samples with our recursive functions © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 16 All Rights Reserved.
  • 17. Tail Recursion Bottom most call's return = Topmost call's return Let's observe the trace on list reversal May not be always possible But if possible, it is a smart compiler advantage Cuts-off processing as soon as lowest level returns © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 17 All Rights Reserved.
  • 18. Example: Set Operations Sets: List of AToms (LATs) Operations: member, union, intersection, adjoin Let's write some examples which support sets being elements of set © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 18 All Rights Reserved.
  • 19. Basic Input / Output Basic Input (read [input-stream] [eof-error] [eof-value]) → s-expr Basic Output (print s-expr [output-stream]) → s-expr (format destination control-string [args]) © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 19 All Rights Reserved.
  • 20. Loading Files Loading Lisp file for interpretation (load "file.lisp") Compiling a Lisp file (compile "file.lisp") or (compile "file") Loading a compiled Lisp file (load (compile "file.lisp")) © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 20 All Rights Reserved.
  • 21. References Common Lisp: http://www.lisp.org CLISP: http://clisp.cons.org Practical Common Lisp by Peter Seibel Also @ http://www.gigamonkeys.com/book/ LISP Tutorial: http://www.mars.cs.unp.ac.za/lisp/ © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 21 All Rights Reserved.
  • 22. What all have we learnt? W's of LISP Language Specifics Demonstration Data Structures Basic Operations Control Structures Basic I/O Fun with Recursion Power, Tail Recursion, Tracing & Analysis © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 22 All Rights Reserved.
  • 23. Any Queries? © 2010 Anil Kumar Pugalia <email@sarika-pugs.com> 23 All Rights Reserved.