Logic (Prolog) as the First
Programming Language
Arthur Fleck
Professor Emeritus
University of Iowa
Frontiers in Education 2007
1
OVERVIEW
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•
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•
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Logical basis
Logic/Prolog programming ideas
Advantages for the first course
Technical course details
Experience and Conclusions
2
Logical basis
• Basic Boolean ops
• And, or, and not, but
written in the notation
of logic ,,
• Logical implication
• A critical Boolean
operation in logic 
• Approached as formal
logic (truth tables)
3
Logical basis
• Predicates/relations
• broOf(john_kennedy,
robert_kennedy)
• Existential and
universal
quantification
• In logic  and  X.broOf(X,
robert_kennedy)
4
Logical basis
• Syntax of well-formed formulas (and
to a large extent, programs too), ideas
of satisfiability and tautology
• Axioms and (sound) proof rules
modus ponens -given formulas a and a  b,
conclude b
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Logical basis
• Truth vs. proof
truth -- dependence on unlimited
values of logic variables makes
direct determination impossible
proof -- concludes truth from analysis
of formula syntax, is independent
of variable values, and requires no
truth evaluation
6
OVERVIEW
• Logical basis
•
•
•
•
Logic/Prolog programming ideas 
Advantages for the first course
Technical course details
Experience and Conclusions
7
Prolog programming ideas
• A program consists of a collection of
universally quantified logical assertions -axioms that characterize the essential
properties of the problem domain
• Solutions are computed by proving logical
consequences of the chosen axioms
8
Prolog programming ideas
• Prolog programs are invoked through
queries -- existentially quantified logical
assertions
• A Prolog programming system determines if
a query is a logical consequence of the
program -- and if so, values of constituent
unknowns must also be reported
9
Prolog programming example
cousin(X,Y) :grandFather(X,GF), grandFather(Y,GF),
grandMother(X,GM), grandMother(Y,GM).
?- cousin(carolineKennedy, C).
C= carolineKennedy
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Corrected Prolog example
• cousin(X,Y) :grandFather(X,GF), grandFather(Y,GF),
grandMother(X,GM), grandMother(Y,GM),
father(X,F1), father(Y,F2), F1\==F2.
• ?- cousin(carolineKennedy,C). % yields
C=mariaSriver -- and many more
• ?- cousin(C,mariaSriver). % yields
C= carolineKennedy -- and many more
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OVERVIEW
• Logical basis
• Logic/Prolog programming ideas
• Advantages for the first course 
• Technical course details
• Experience and Conclusions
12
Prolog programming advantages
• Higher-level abstraction -- focus is on
essential properties
• Example -- list concatenation relation
append([ ], Suf, Suf).
append([X|Pre], Suf, [X|Join])
:- append(Pre, Suf, Join).
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Prolog programming advantages
• The 'append' assertions comprise several
traditional programs -?- append([a,b], [c,d], Ans). % yields
Ans=[a,b,c,d]
?- append(Ans, [c,d], [a,b,c,d]). % yields
Ans=[a,b]
?- append(Ans1, Ans2, [a,b,c,d]). % yields
Ans1=[ ], Ans2=[a,b,c,d] and
Ans1=[a], Ans2=[b,c,d] and …
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Prolog programming advantages
• Logic programming emphasizes modeling
and abstraction
• Precision in thinking and accuracy in
programming are simultaneously achieved
• Programming and problem solving become
tightly integrated
• The relational programs are innately much
more general and reusable
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OVERVIEW
• Logical basis
• Logic/Prolog programming ideas
• Advantages for the first course
• Technical course details 
• Experience and Conclusions
16
Course details
• First phase - introduce logic
1. Discuss formula syntax and use
of truth tables
2. Emphasize differences (e.g.,
domains, quantifiers) found in
predicate logic
3. Explain the relationship between
proof and truth evaluation
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Course details
• Second phase - use Prolog to animate
logic
1. use logic formulas as syntax guide,
start with familiar examples
(e.g., genealogical relations)
2. emphasize relational character
3. recursion is natural and raises no
conceptual complications
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Course details
• Third phase - introduce Prolog's
backtracking search strategy for proofs
1. Require substantial student use of
the Prolog trace facility
2. Discuss e.g. success/failure loops
and negation as failure with this
procedural model
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Course details
• Fourth phase - gain experience with
integration of multiple features
1. Compare the several means of
expressing repetitive computation
2. Study the complication of deducing
implications of negative assertions
3. Projects solving logic puzzles are
sources requiring varied facilities
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OVERVIEW
•
•
•
•
Logical basis
Logic/Prolog programming ideas
Advantages for the first course
Technical course details
• Experience and Conclusions 
21
Experience
• An elective course, open only to
college freshmen, was taught for six
years
• Students readily handled the formal
logic
• The interactive and incremental style
of Prolog programming promoted
student success
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Conclusions
• Students enjoyed logic/Prolog programming,
and their performance met or exceeded that in
the traditional first course
• Analytical emphasis supports programming in
whatever language follows next
• The goal to reveal an intrinsic link between
analytical thinking and computer solutions to
problems is well served
• Logic programming is a superior choice for
students first programming course
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