= Nondeterminism =

This is a Chicken Scheme egg which implements nondeterministic
computation. Note that its results are deterministic, there are no
calls to rand(). Originally from Jeff Siskind's QobiScheme.

Examples are available in the ''examples/'' directory.

=== Generation ===

:(a-boolean)
:(an-integer-above i)
:(an-integer-below i)
:(an-integer)
:(an-integer-between i j)
:(a-member-of list)
:(a-subset-of list)
:(a-split-of list)
:(a-permutation-of list)
:(a-partition-of list)
:(a-partition-of-size size list)

Generate a number of different kinds of elements.

:(either a b)

Select either a or b, everything is built on top of this primitive.

:(fail)

Backtrack at this point.

=== Execution ===

:(for-effects . body)

Execute a nondeterministic computation only for its effects not its
result.

:(all-values . body)

Execute a nondeterministic computation and produce a list of
all of its possible outputs.

:(one-value . body
:(local-one-value . body)

Execute a nondeterministic computation, return one output,
and discard the rest of the computation.

:(possibly? . body)

Execute a nondeterministic computation and return #f if it always
fails.

:(necessarily? . body)

Execute a nondeterministic computation and return #f if it can fail.

=== Side-effects ===

:(unwind-trail)
:(unwedge-trail)

Pop the stack once or clear it entirely.

:(local-set! obj val)
:(local-set-car! x y)
:(local-set-cdr! x y)
:(local-string-set! s i x)
:(local-vector-set! v i x)

Perform operations with side-effects that will be undone when backtracking.

:(upon-failure . body)

When backtracking execute ''body'', the above operations are implemented
in terms of this primitive.

=== Low-level features ===

:<nowiki>*</nowiki>fail?*
:(top-level-fail)
:(set-fail! f)

Internal

=== License ===

   Copyright 1993-1995 University of Toronto. All rights reserved.
   Copyright 1996 Technion. All rights reserved.
   Copyright 1996 and 1997 University of Vermont. All rights reserved.
   Copyright 1997-2001 NEC Research Institute, Inc. All rights reserved.
   Copyright 2002-2012 Purdue University. All rights reserved.
   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
   You should have received a copy of the GNU General Public License
   along with this program.  If not, see http://www.gnu.org/licenses.
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