Yield Prolog: 1.0.4 Released

Embed Prolog directly in your Python, C# or Javascript program using the yield keyword. There is no API standing between your code and Yield Prolog, so you can use all language features, including arrays, file I/O, user interaction and your own classes.

Release 1.0.4 is a maintenance release to fix some outstanding bugs in the Bugs tracker.
Fixed Bugs:
* 2720953: Wrong result in C# for bagof(a, (Y = f(1) ; Y = f(1)), B).
* 2553270: In query editor, X = 1, L = f(X) doesn't show value for L.
* 2546578: clause/2 needs copy_term.

This release has full support in Python, C# and Javascript for parser, compiler, dynamic predicates and an interactive shell (except the Python interactive shell is forthcoming).

As usual, download at:

Try the Javascript query editor at

Or download the package and try the interactive YPShell.exe in the folder YieldProlog\bin.

Python is supported in Python 2.5.

C# is supported in Visual C# (Windows).
Mono support is incomplete until Mono 2.0 is released which includes this bug fix:

Javascript is supported in Firefox 3, which fully supports the yield keyword.
Seamonkey support is incomplete until Seamonkey 2 is released which includes this bug fix:

See the documentation including how to use the compiler and module system at:

Known Issues:

Here are the 8 errors of the 421 tests in the ISO test suite in
YieldProlog\source\prolog\isoTestSuite.P .
Some of these have a good excuse for why Yield Prolog produces the error. The rest will be addressed in a future maintenance release.

Goal: call((fail, 1))
Expected: type_error(callable, (fail, 1))
Extra Solutions found: failure

Goal: call((write(3), 1))
Expected: type_error(callable, (write(3), 1))
Extra Solutions found: type_error(callable, 1)

Goal: call((1; true))
Expected: type_error(callable, (1 ; true))
Extra Solutions found: type_error(callable, 1)

Goal: (catch(true, C, write('something')), throw(blabla))
Expected: system_error
Extra Solutions found: unexpected_ball(blabla)

Goal: Goal: (X = 1 + 2, 'is'(Y, X * 3))
Expected: [[X <-- (1 + 2), Y <-- 9]]
Extra Solutions found: type_error(evaluable, /(+, 2))

Goal: 'is'(77, N)
Expected: instantiation_error
Extra Solutions found: N <-- 77)

Goal: \+(!, fail)
Expected: success
Extra Solutions found: failure

((X=1;X=2), \+((!,fail)))
Expected: [[X <-- 1],[X <-- 2]]
Extra Solutions found: failure

Posted by Jeff Thompson 2009-07-26

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