Prolog for Linguists Symbolic Systems 139P/239P

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Prolog for Linguists Symbolic Systems 139P/239P

• John Dowding
• Fall, 2001

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Goals

• Gain basic competence in Prolog programming.
• Understand relationships between Prolog, Logic,
  Logic Programming, and Linguistics.
• Understand when to (and not to) consider using
  Prolog.

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Course Requirements

• Homework assignments most weeks
• 3 assignments to be handed in (50)
• Term manipulation
• Definite Clause Grammars
• TBD
• Final project (50)
• Ill provide some examples
• 239P should write up a final project proposal,
  and present project in class.

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Textbook

• Programming in Prolog, 4th edition, 1994
• Clocksin and Mellish
• ISBN 3-540-58350-5

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Course web page

• http//www.stanford.edu/class/symbsys139p
• programs used in class
• power point slides
• homework assignments, solutions

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Office Hours

• We have reserved 4 workstations in Meyer Cluster,
  in Meyer library
• 430-530 on Thursday

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Course Schedule

• Oct. 8
• Oct. 15
• Oct. 22
• Oct. 29
• Nov. 5
• Nov. 12
• Nov. 26
• Dec. 3
• No class on Nov. 19
• We need to make up 2 classes

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Running Prolog at Stanford

• Use Sicstus Prolog 3.8.6
• On elaine, installed in
• /afs/ir/class/symbsys139p/bin
• Add to your path, and run as
• sicstus
• Talk to me about installing Sicstus prolog on
  your personal Windows or Linux laptop or
  workstation.

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History

• Automatic Theorem Proving
• Robinson 1965
• PROgramming in LOGic
• Kowalski, 1974
• Deduction as computation
• Prolog, Colmerauer, Marseille, 1973
• Edinburgh Prolog, 1977
• Prolog 10, David Warren
• Warren Abstract Machine
• ClocksinMellish, 1981

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History (cont.)

• Japanese 5th Generation Project
• 1981
• Quintus Corporation
• 1st Industrial strength Prolog implementation
• ISO Prolog Standard, 1994
• P. Deransart, et al.

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What kind of a thing is Prolog?

• Very different from C, C, Java, and other
  Procedural languages
• Symbolic Programming Language
• Logic Programming Language
• Declarative Programming Language
• Database Language

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Database Program Example
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Prolog program

• A Prolog program is defined by a set of
  Predicates
• Each Predicate has a unique Functor and Arity
• parent(Parent, Child)
• a predicate whose functor is parent with arity
  2.
• Each Predicate is defined by a sequence of
  Clauses
• A Clause is either a Fact or a Rule
• fact().
• head() - goal1(), , goalN().
• Each argument to a predicate is a Term

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Terms

• Each argument to a predicate is a Term
• A Term is either
• Atomic
• Variable
• Compound

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Atomic terms

• Atomic terms can be either atoms or numbers
• Atoms can be a sequence of alphanumeric
  (including _) characters starting with a lower
  case letter, or a sequence of any characters
  embedded in single quote marks
• johnDowding symbsys139p quoted atom
  non_quoted_atom
• Numbers can be integers or floating point
• Well look at numbers at a later time

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Variables

• Variables start with a capital letter or _
  character
• X Parent _Sibling _
• Variables can stand in for arbitrary Prolog terms
  (including other variables)
• Variables that occur with the same name in the
  same clause represent the same variable, except
  for
• The anonymous variable _, which always
  represents a unique variable.

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Compound Terms

• A compound term is a structure with a functor
  and N arguments.
• functor(Arg1, Arg2, , ArgN)
• Each argument can be an arbitrary Prolog term

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Example Successor Arithmetic

• Simple arithmetic using compound terms to
  represent integers
• 0 0
• 1 s(0)
• 2 s(s(0))
• 3 s(s(s(0)))
• 4 s(s(s(s(0))))
• .
• .
• .

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Structural Induction and Recursion

• Inductive proofs have a base (or terminating)
  case and an inductive step.
• Mathematical induction over the space of
  integers
• Structural induction over subsets of the space
  of Prolog Terms.
• Many Prolog predicates have this structure
• is_number(0).
• is_number(s(Number)) - is_number(Number).

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Show successor arithmetic example
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BUILT-IN Predicate compile/1

• compile(FileName)
• Load the Prolog program in FileName into memory.

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Homework

• Learn how to run SICStus Prolog
• Type in and query a small database problem
• Read Chapters 12 of ClocksinMellish
• Write predicates for successor arithmetic
• exponential(Number, Exponent, ?Result)
• factorial(Number, ?Factorial)