View source for CLP(R)

{{Short description|Constraint logic programming over rational and real numbers}}
'''CLP(R)''' is a [[declarative programming language]]. It stands for [[constraint logic programming]] (real) where real refers to the [[real number]]s. It can be considered and is generally implemented as a superset or add-on package for a [[Prolog]] implementation.

==Example rule ==
The [[simultaneous linear equations]]:
:<math>\begin{cases}
3x + 4y - 2z = 8\\
x - 5y + z = 10\\
2x + 3y -z = 20
\end{cases}</math>
are expressed in CLP(R) as:

<syntaxhighlight lang="prolog">
3*X + 4*Y - 2*Z = 8,
X - 5*Y + Z = 10,
2*X + 3*Y -Z = 20. 
</syntaxhighlight>

and a typical implementation's response would be:<br>

<samp>
Z = 35.75<br>
Y = 8.25<br>
X = 15.5<br>
<br>
Yes<br>
</samp>

==Example program==

CLP(R) allows the definition of predicates using recursive definitions. For example a ''mortgage'' relation can be defined as
relating the principal P, the number of time periods of the loan T, the repayment each period R, the interest rate per period I
and the final balance owing at the end of the loan B.
<syntaxhighlight lang="prolog">
mg(P, T, R, I, B) :- T = 0, B = R.
mg(P, T, R, I, B) :- T >= 1, P1 = P*(1+I) - R, mg(P1, T - 1, R, I, B).
</syntaxhighlight>
The first rule expresses that for a 0 period loan the balance owing at the end is simply the original principal.
The second rule expresses that for a loan of at least one time period we can calculate the new owing amount P1 by 
multiplying the principal by 1 plus the interest rate and subtracting the repayment.  The remainder of the loan
is treated as another mortgage for the new principal and one less time period.

What can you do with it?  You can ask many questions.
If I borrow 1000$ for 10 years at 10% per year repaying 150 per year, how much will I owe at the end?
<syntaxhighlight lang="prolog">
?- mg(1000, 10, 150, 10/100, B).
</syntaxhighlight>
The system responds with the answer
<syntaxhighlight lang="prolog">
B = 203.129.
</syntaxhighlight>

How much can I borrow with a 10 year loan at 10% repaying 150 each year to owe nothing at the end?
<syntaxhighlight lang="prolog">
?- mg(P, 10, 150, 10/100, 0).
</syntaxhighlight>
The system responds with the answer
<syntaxhighlight lang="prolog">
P = 921.685.
</syntaxhighlight>

What is the relationship between the principal, repayment and balance on a 10 year loan at 10% interest?
<syntaxhighlight lang="prolog">
?- mg(P, 10, R, 10/100, B).
</syntaxhighlight>
The system responds with the answer
<syntaxhighlight lang="prolog">
P = 0.3855*B + 6.1446 * R.
</syntaxhighlight>
This shows the relationship between the variables, without requiring any to take a particular value.

== Prolog Integration ==
CLP(R) has first been integrated into a Prolog system in 1994, namely into [[SICStus|SICStus Prolog]].<ref>{{Cite journal |last=Holzbaur |first=Christian |date=1995 |title=OEFAI clp(q,r) Manual Revision 1.3.2 |url=http://www.ai.univie.ac.at/cgi-bin/tr-online?number+95-09 |journal=ÖFAI Technical Reports Online |issue=95–09|archive-url=https://web.archive.org/web/20010520132506/http://www.ai.univie.ac.at/cgi-bin/tr-online?number+95-09 |archive-date=20 May 2001 }}</ref> This implementation has since been ported to many popular Prolog systems, including [[Ciao (programming language)|Ciao]],<ref>{{Cite web |title=Introduction — The Ciao System v1.22 |url=https://ciao-lang.org/ciao/build/doc/ciao.html/ciaointro.html |access-date=2023-11-06 |website=ciao-lang.org}}</ref> [[SWI-Prolog]]<ref>{{Cite web |title=SWI-Prolog manual |url=https://www.swi-prolog.org/man/clpqr.html |access-date=2023-11-06 |website=www.swi-prolog.org}}</ref> and [[XSB]].<ref>{{Cite book |last=Swift |first=Theresa |title=The XSB System, Version 5.0, Volume 2: Interfaces and Packages |date=13 May 2022 |pages=71 |chapter=Constraint Packages}}</ref> 

== See also ==
* [[Comparison of Prolog implementations]]
* [[Prolog syntax and semantics]]

==References==
{{Reflist}}
* Joxan Jaffar, Spiro Michaylov, Peter J. Stuckey, Roland H. C. Yap: [http://doi.acm.org/10.1145/129393.129398 The CLP(R) Language and System]. [[ACM Transactions on Programming Languages and Systems]] 14(3): 339-395 (1992)

==External links==
* [http://www.sju.edu/~jhodgson/clp/howto_clpr.html How To CLP(R)] {{Webarchive|url=https://web.archive.org/web/20080914035015/http://www.sju.edu/~jhodgson/clp/howto_clpr.html |date=2008-09-14 }}
* [http://www.sju.edu/~jhodgson/clp/manualclp.pdf CLP(R) Programming Manual] {{Webarchive|url=https://web.archive.org/web/20051103170702/http://www.sju.edu/~jhodgson/clp/manualclp.pdf |date=2005-11-03 }}

[[Category:Prolog programming language family]]
[[Category:Constraint logic programming]]


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