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This namespace SbsSW.SwiPlCs provides an .NET interface to SWI-Prolog
Overview
Prolog variables are dynamically typed and all information is passed around using the C-interface type term_t witch is an int. In C#, term_t is embedded in the lightweight struct PlTerm. Constructors and operator definitions provide flexible operations and integration with important C#-types (string, int and double).
The list below summarises the important classes / struct defined in the C# interface.
| class / struct | Short description |
|---|---|
| PlEngine | A static class represents the prolog engine. |
| PlTerm | A struct representing prolog data. |
| PlTermV | A vector of PlTerm. |
| PlQuery | A class to query Prolog. |
Types| All Types | Classes | Structures | Enumerations |
| Icon | Type | Description | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
 | PlEngine |
This static class represents the prolog engine.
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| PlFrame | The class PlFrame provides an interface to discard unused term-references as well as rewinding unifications (data-backtracking). Reclaiming unused term-references is automatically performed after a call to a C#-defined predicate has finished and returns control to Prolog. In this scenario PlFrame is rarely of any use. This class comes into play if the top level program is defined in C# and calls Prolog multiple times. Setting up arguments to a query requires term-references and using PlFrame is the only way to reclaim them. | ||||||||||
| PlQuery | This class allows queries to prolog. A query can be created by a string or by constructing compound terms see Constructors for details. All resources an terms created by a query are reclaimed by Dispose()()()(). It is recommended to build a query in a using scope. There are four possible opportunities to query Prolog
For examples see PlQuery(String) and PlQuery(String, PlTermV) | ||||||||||
 | PlQuerySwitch |
Flags that control for the foreign predicate parameters
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| PlQueryVar |
Represents one variable of a Query result.
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| PlQueryVariables | Represents the set variables of a Query if it was created from a string. This class is also used to represent the results of a PlQuery after ToList()()()() or SolutionVariables was called. | ||||||||||
 | PlTerm | The PlTerm struct plays a central role in conversion and operating on Prolog data. PlTerm implements IComparable to support ordering in [!:System.Linq] queries if PlTerm is a List. Creating a PlTerm can be done by the Constructors or by the following static methods: PlVar(), PlTail(), PlCompound, PlString(), PlCodeList(), PlCharList() (see remarks) | ||||||||||
| PlTermV | The struct PlTermv represents an array of term-references. This type is used to pass the arguments to a foreign defined predicate (see DelegateParameterVarArgs), construct compound terms (see PlCompound(String, PlTermV) and to create queries (see PlQuery). The only useful member function is the overloading of [], providing (0-based) access to the elements. Item[([( Int32])]) Range checking is performed and raises a ArgumentOutOfRangeException exception. | ||||||||||
| PlType |
Obtain the type of a term, which should be a term returned by one of the other
interface predicates or passed as an argument. The function returns the type of
the Prolog term. The type identifiers are listed below.
|
ExamplesBefore going into a detailed description of the CSharp classes let me present a few examples illustrating the `feel' of the interface. The Assert class in the sample is from the test framework and has nothing to do with the interface. It shows only which return values are expected.
Creating terms
This very simple example shows the basic creation of a Prolog term and how a Prolog term is converted to C#-data:
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|---|---|
PlTerm t1 = new PlTerm("x(A)"); PlTerm t2 = new PlTerm("x(1)"); Assert.IsTrue(t1.Unify(t2)); Assert.AreEqual("x(1)", t1.ToString()); | |
Calling Prolog
This example shows how to make a simple call to prolog.
| Copy | |
|---|---|
PlTerm l1 = new PlTerm("[a,b,c,d]"); Assert.IsTrue(PlQuery.PlCall("is_list", l1)); | |
Getting the solutions of a query
This example shows how to obtain all solutions of a prolog query.
PlQuery takes the name of a predicate and the goal-argument vector as arguments. From this information it deduces the arity and locates the predicate. the member-function NextSolution() yields true if there was a solution and false otherwise. If the goal yielded a Prolog exception it is mapped into a C# exception.
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|---|---|
PlQuery q = new PlQuery("member", new PlTermV(new PlTerm("A"), new PlTerm("[a,b,c]"))); while (q.NextSolution()) Console.WriteLine(s[0].ToString()); | |
There is an other constructor of PlQuery which simplify the sample above.
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|---|---|
PlQuery q = new PlQuery("member(A, [a,b,c])"); foreach (PlTermV s in q.Solutions) Console.WriteLine(s[0].ToString()); | |
An other way to get the results is to use SolutionVariables to iterate over PlQueryVariables.
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|---|---|
PlQuery q = new PlQuery("member(A, [a,b,c])"); foreach (PlQueryVariables vars in q.SolutionVariables) Console.WriteLine(vars["A"].ToString()); | |
It is also possible to get all solutions in a list by ToList()()()(). This could be used to work with LinQ to objects which is really nice. PlQuery and ToList()()()() for further samples.
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|---|---|
var results = from n in new PlQuery("member(A, [a,b,c])").ToList() select new {A = n["A"].ToString()}; foreach (var s in results) Console.WriteLine(s.A); | |