Logic Programming & Prolog
                                          RRiiccararddoo  RRoocchhaa
                                     Computer Science Department
                                  Faculty of Sciences, University of Porto
            Implementation of Programming Languages
                                          2019/2020
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 Declarative Languages
   Logic programming languages, together with functional programming
   languages,formamajorclassoflanguagescalleddeclarativelanguages.
   Acommoncharacteristicofbothgroupsoflanguagesisthattheyhavea
   ssttrroonngg mmaatthheemmaattiiccaall bbaassiiss::
       • Logicprogramminglanguagesarebasedonthepredicatecalculus
       • Functionalprogramminglanguagesarebasedonthelambdacalculus
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 Declarative Languages
   Declarative languages are considered to be very high-level languages
   when compared with conventional imperative languages because,
   generally, they allow the programmer to concentrate more on what the
   problem is, leaving much of the details of how to solve the problem to
   tthhee ccoommppuutteerr..
   The programmer specifies the problem at a more application-oriented
   level, which simplifies the formal reasoning about it.
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 Logic Programming
   Logic programming is a programming paradigm based on Horn Clause
   Logic, a subset of First Order Logic.
   Logic programming is a simple theorem prover that given a theory (or
   program) and a query, uses the theory to search for alternative ways to
   ssatatiissffyy tthhee qquueerryy::
       • Variablesarelogicalvariables which canbeinstantiatedonlyonce
       • Variablesareuntypeduntilinstantiated
       • Variables are instantiated via unification, a pattern matching operation finding
           themostgeneralcommoninstanceoftwodataobjects
       • At unification failure the execution backtracks and tries to find another way to
           satisfy the original query
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