CSE583: Programming Languages

2/15/00

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Table of Contents

CSE583: Programming Languages

Two weeks: logic and constraint logic programming paradigms

(Symbolic) Logic

Predicate logic and English

Tautologies and contradictions

Prolog deals with relations

History of Prolog

Not for general purpose programming

Why restrict applicability of a language?

Example applications

A Prolog Program

Example facts and simple queries

Syntax for facts

Variables are scopedwithin a query

Two interpretations of rule

Eight Queens:A typical search problem

A Solution to Eight Queens

Eight Queens in Prolog

Query for solution

Our friend the list

Declaration of append rule

“Return value”is an argument of the rule

Lists need not behomogeneous

Unification of terms

Unification of terms S and T

More unification examples

Unification is implicitin rule application

Unification in append rule

Trace of app([1,2,3],A,[1,2,3,4])

Trace of app([1,2,3],[4],Z)

Why this limitation?

Arithmetic in Prolog

Change for a dollar: J.R. Fisher

Arithmetic onlyworks forward in Prolog

Definition of member

The declarative interpretation falls short…

More uses of member

Reminder: How Prolog tries to prove

Evidence of top to bottomrule order

Order of rules matters!

Trace of mem1(2,[1,2,3])

Trace of mem2(2,[1,2,3])

mem1 was faster

Prolog is not an oracle!

Search algorithm

Multiple sub-goals

Another search tree…

Tracing through the tree

Backtracking is notalways what we want

delete_all example

A query for delete_all

delete_all can succeedin any of three ways...

delete_all has multiple matching rules

Third rule contained implicit assumption

Use a “cut” — !

The query again

Cut divides probleminto backtracking regions

Controversy over cut

!, fail combination

Tree view of a cut

Tree view of a cut

Expression evaluation

Writing generators

In some sense, that’s it

Other cool things

Next week: CLP(R)

Author: David Notkin

Email: notkin@cs.washington.edu

Home Page: http://www.cs.washington.edu/education/courses/583

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