Lisp Slides

7/23/2019 Lisp Slides

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FunctionalProgramming


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Functional programming

The primary method of computation is the

application of functions to arguments

Immutable & stateless

Allows less error, cleaner, and elegant code


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Problem domain

Academic Discussion

Mathematical Evaluation

Software Simulation Training (AI)

Financial Computation

Web Development Hardware Design


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History and evolution

at the very foundation, the basis of most

functional programming language is

Lambda Calculus

a formal system in mathematical logic

(especially in computational)

theoretical framework for describing

functions & their evaluation


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Existing languages Lisp

early functional language. introduced several

features for functional-flavored programming

languages Intermediate Programming Language(IPL)

first computer based functional programming language.

assembly-styled FORTRAN

Hope

Rex


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Important

conceptsIn functional programming


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First class and higher order functions

FC: ComSci

HO: Math

Functions that take in functions as arguments

Differential operator


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First class and higher order functions

Application

Partial Application and Currying:

applying arguments one at a time, returning a newfunction that takes the next argument

a + b * c a.add(b.multiply(c))


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Recursion

Iteration is often expressed

as recursion

Tail Recursion:

the function is called at the end of the function

often optimized in Functional Programming during

compilation


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Pure functions

Functions that only returns a value

do not modify any state, like changing thevalue of a global variable

this restricted action is called a side effect


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Pure functions

Allows For Optimization

removal run in parallel (threading)

function reordering memoization


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evaluation

StrictFail at 1/0

non-strict4

print length([2+1, 3*2, 1/0, 5-4])

WHY?


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evaluation

StrictEvaluates everything

non-strictOnly evaluates when needed

print length([2+1, 3*2, 1/0, 5-4])


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LISP


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LIST PROCESSING


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LIST PROCESSING


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1956 1958 1981

second-oldest programming language that is still in widespread use

Next toFORTRAN


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19561958 1981

CONCEPTUALIZED


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lisp Initially designed for performing mathematical

notations

LAMBDA CALCUluS

Favored by researchers in Artificial Intelligencefor its capacitY and support for s y m b o l i c

programming

1956 1958 19811958

A l o n z o C h u r c h


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lisp Initially designed for performing mathematical

notations

LAMBDA CALCUluS

Favored by researchers in Artificial Intelligencefor its capacitY & support for s y m b o l i c

programming

1956 1958 19811958


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MacLisp ZetaLisp

Scheme Interlisp

DIALECTS OF lisp

1956 1958 1981

1980s


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LISP MACHINES Runs entirely on lisp Need for power to run

complex aI software

Distributed bycompanies with

their own versions

First single-userworkstations

1956 1958 1981

1980s


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1956 1958

COMMON LISP PROBLEM: large number of lisp dialects

May cause lisp community

Solution: standardize a new language

Have best features of lisp dialects

1981


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PROGRAMMING PARADIGMS

Functional Procedural

Reflective Meta


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BASIC STRUCTURE

( )


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Symbolic expressions

3 valid objects:ATOMLIST

STRING

LISP EXPRESSIONS


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LIST

()

(yo)

(atom1 atom2)

(atom1 (atom2inlist) atom3)


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SPECIAL SYMBOLS

Tset of all objects (True, yes, 1)

nilempty data type (False, no, 0)


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Read-Evaluate-print-loop

REPL

Check source code in repeated loop

Reads symbolic expression, evaluatesit, and prints the result


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PREFIX NOTATION

Operands come after the operators

(+ 2 3)

(+ 1 2 3)


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NAMES Identifiers are symbols (variables in

terms of form)

composed of alphanumeric characters,underscores, and hyphens

this-asymbol_5

anothersymbol


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LIFETIME

Dynamic variables in Lisp have indefinite

lifetimes stay until everything finishesrunning

Variables bound with let only last untilthe end of the defining form


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Data Types

Set of objects

Each object belongs to at least onedata type

Explicit declaration of data type isnot necessary


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FUNCTIONS ON Data Types

Typepdetermines if a certain object belongs to a certain

set/data type which returns a value of t if itbelongs to the set and nil if not

Type-ofReturns data type of an object


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Data types: numbers

Integer fixnum - expressible within machine range (e.g. 1, -1, 500)

bignum - integers that do not fall under fixnum (e.g. 25!)

Ratiofractional form of a/b expressed in code as / a b)

Floating point

decimal form (e.g. 4.589, -10.2, 3.00.)

Complex numbersnumbers with imaginary components a+bi is expressed as #C(a b)


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Data types: characters

Standard characters

begin with #\ followed by any of the following characters:

! @ # $ % & * + ( ) - , . / < > ? ; : { }\ ~ [ ] | ^ _ = `

A.Z

a.z

0...9

Special characters#\Backspace, #\Tab, #\linefeed


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Data types: others

Arrays

Vectors

Hash tablesseries of elements with key and value component

Listmost important data type since lisp is heavy on list processing


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If

Progn is used to block multiple statements &

returns the value of the final statement


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case


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LOOP for


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do


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subprograms


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STRENGTHS AND

WEAKNESSES


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Strengths

Garbage Collection

Dynamic Typing

Support for macros

every programmer can make his own extension

Powerful Error Handling

signaling

handling

restarting


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Strengths

Decent Performance

relative to C++, Lisp is slower by just 1-2 times

compared to Python which is 2-100 times slower.

Portable across hardware and OS


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Weaknesses

Support for macros

Common Lisp

Scheme

Clojure

Dynamic Typing

strong vs weak typing


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Comparative

critique


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WITH SCHEME

Scheme more minimalisticCommon Lisp more functions

More numerical support on Lisp

Tail calls are optimized in Scheme, possible inCommon Lisp but not required


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WITH SCHEME

Scheme has one namespace

Common Lisp has separate namespacesfor functions and objects (i.e.

you may have a function andan object with the same name)


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WITH python

One namespace in PythonPython has distinctions for statements and

expressions; everything in Common Lisp is an expression

Objects are prevalent in both languages

Both languages employ automatic garbage collection


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CURRENT

IMPLEMENTATIONS


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Current implementations Several other implementations of Lisp exist apart from

Common, including:

1. CLISP

2. CMUCL (main goal is ANSI compatibility)3. ECL (Embeddable CL)4. CCL (Clozure CL)5. SBCL6. ABCL (Armed Bear CL, runs on Java)7. MKCL


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Real life applications

Authorizers Assistant is a system

used by American Express for

authorizing transactions


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SPIKE schedules the observationperiods of NASAs Hubble Space

Telescope


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The visual language PWGL is used for

synthesizing sounds & aiding

musical composition



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Mirai, a 3D animation suite, was used to animate the

face of Gollum


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DEMO


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Quiz

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