LISP

1
LISP Not just a Speech Impediment

• Jim Lowe

2
Brief History of LISP

• Initial development begins at the Dartmouth
  Summer Research Project in 1956 by Dr John
  McCarthy.
• At the time, Fortran was the only high level
  programming language available.
• Dr. McCarthy and his colleagues were interested
  in producing a language more suited for
  manipulating data in a similar manner to human
  thought.Artificial Intelligence.
• Language development was completed at MIT and was
  made available to the general computer science
  community in 1963.

3
Innovations of LISP

• First functional language.
• Emphasis is on the evaluation of expressions
  rather than the execution of commands.
• Recursion
• The concept of a function calling itself until a
  predefined base case was reached was a
  significant step forward in CS. LISP memory
  management was developed to allow for recursion.
• Recursion was a mathematical concept applied to a
  computer.
• Object Orientation
• The basic unit of data in LISP is a list. This
  data structure is ideally suited for definition
  of a weak typed object. For example, animals
  could be defined as
• (animals (cat brown) (dog white) (bird purple))
• (animals (cat brown dumb) (dog white smart))

4
Inovations of LISP (cont.)

• Object Orientation (cont)
• This concept was developed to provide for
  programming a computer to think like a human
• Functions can be defined as objects and passed as
  arguments.
• Garbage Collection
• Memory management was handled by the interpreter.
• Conditionals
• A conditional is an if-then-else construct. We
  take these for granted now.
• FORTRAN used GOTO
• Variables
• In LISP all variables are pointers, this allowed
  for the reduction of data storage requirements
  for recursive functions.

5
LISP BNF Grammar

• All LISP expressions built from simple grammar
  rules
• Atom NULL OR Letter OR Number
• Letter A OR B OR C.OR Z
• Number 0 OR 1 or 2 OR 9
• S-Expression Atom OR (S-Expression .
  S-Expression) OR List.
• List (S-Expression )
• NULL
• Atoms can be used to represent values and passed
  as these values. For example we may need to
  define PI to equal 3.1415 or FRED to equal
  Fredrick the 3rd of Nowhere. To do this, LISP
  binds a value to the variable representation.
  With the function setq.

6
Functionality of LISP

• LISP can be compiled or interpreted.
• Early LISP was interpreted only. This was of
  particular importance due to a complete lack of
  computer operating system standardization.
• Later versions (c. 1968) provided for compilation
  to take advantage of LISP machines. LISP
  Machines were computers built solely to execute
  LISP instructions.
• Variable visibility is limited to descendants
  from point of definition
• There is no real distinction between read-time,
  compile-time, and runtime.
• You can compile or run code while reading, read
  or run code while compiling, and read or compile
  code at runtime.

7
LISP today

• LISP is currently standardized in many different
  forms.
• ANSI standard X3.226
• ISI (International Standards Institute)
  13816.1997
• Many of the descendants of LISP are also
  standardized.
• Scheme Educational and Research language.
• Arc A modern LISP derivative.
• AutoLISP A dialect used for CAD applications.
• Dylan An object-oriented dialect of LISP.
• Emacs LISP Text editor extension language.

8
Advantages of LISP

• Programs are easy to test due to interactive
  interpreter environment.
• Portable across hardware platforms with supported
  interpreters.
• Clear and concise syntax and semantics.
• Automatic memory management and garbage
  collection.
• Packaging of programs into modules.
• Flexible data structures.
• Object oriented capability.

9
Disadvantages of LISP

• Limited availability of compilers Increased
  program size and run time.
• Cross platform compatibility requires multiple
  interpreter environments.
• Small install base creates limited audience for
  programs.
• Other computer programmers make fun of you
  because you talk funny.