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JPL - Java <-> SWI Prolog Interface

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JPL is a set of Java classes and C functions providing a bidirectional interface between Java and Prolog. JPL uses the Java Native Interface (JNI) to connect to a Prolog engine through the Prolog Foreign Language Interface (FLI). JPL is not a pure Java implementation of Prolog; it makes extensive use of native implementations of Prolog on supported platforms.

In its current version, JPL supports the embedding of a Prolog engine within the Java VM as well as the embedding of a Java VM within Prolog, so that, for example, one could take advantage of the rich class structure of the Java environment from within Prolog.

JPL is designed in two layers, a low-level interface to the Prolog FLI and a high-level Java interface for the Java programmer who is not concerned with the details of the Prolog FLI. The low-level interface is provided for C programmers who may wish to port their C implementations which use the FLI to Java with minimal fuss. The current version of JPL only works with SWI-Prolog.

JPL has been integrated into the full SWI-Prolog distribution starting with version 5.4.x and is included in the binary packages provided by Binary packages provided by 3rd parties may differ, not providing JPL or providing it as a separate package.

Further documentation

  • Overview documentation is maintained at this JPL Web Page, which subsumes the Wiki in this repo.
  • The Prolog API reference is provided from the SWI-Prolog manual.


The objectives of JPL are to:

  1. enable Prolog applications to exploit any Java classes, instances, methods etc. (without requiring any wrappers, metadata etc. to be set up first);
  2. enable Java applications to manipulate any Standard Prolog libraries, predicates, etc. (without requiring any wrappers, metadata etc. to be set up first); and
  3. enable hybrid Prolog+Java applications to be designed and implemented so as to take best advantage of both language systems, and to be testable, debuggable, maintainable.

.. while also aim for:

  • minimum impact deployability: runtime support for Prolog+Java apps must be a position-independent, self-sufficient filestore tree, requiring no changes to registries, system libraries, system configuration files etc.
  • minimum dependency deployability: as with JVMs, the Prolog+Java runtime support must depend upon nothing which cannot be taken for granted in healthy OS installations
  • minimum vulnerability deployability: the Prolog+Java runtime support must be immune to legitimate variations in its environment (PATH settings, other applications and libraries including other Prolog+Java apps, etc.)


JPL is released under the terms of the Simplified BSD License. See LICENSE file.