1 ;;; -*- Mode: Lisp; Syntax: ANSI-Common-Lisp; Base: 10; -*-
3 ;;; satwrap.lisp --- SAT solvers wrapped for CL
5 ;; Copyright (C) 2010 Utz-Uwe Haus <lisp@uuhaus.de>
7 ;; This code is free software; you can redistribute it and/or modify
8 ;; it under the terms of the version 3 of the GNU General
9 ;; Public License as published by the Free Software Foundation, as
10 ;; clarified by the prequel found in LICENSE.Lisp-GPL-Preface.
12 ;; This code is distributed in the hope that it will be useful, but
13 ;; without any warranty; without even the implied warranty of
14 ;; merchantability or fitness for a particular purpose. See the GNU
15 ;; Lesser General Public License for more details.
17 ;; Version 3 of the GNU General Public License is in the file
18 ;; LICENSE.GPL that was distributed with this file. If it is not
19 ;; present, you can access it from
20 ;; http://www.gnu.org/copyleft/gpl.txt (until superseded by a
21 ;; newer version) or write to the Free Software Foundation, Inc., 59
22 ;; Temple Place, Suite 330, Boston, MA 02111-1307 USA
32 (in-package #:satwrap
)
36 (defclass sat-solver
()
37 ((backend :initarg
:backend
:accessor sat-solver-backend
)
38 (numvars :initform
0 :accessor sat-solver-numvars
)
39 (clauses :initform
'() :accessor sat-solver-clauses
) ;; CNF
41 (:default-initargs
:backend
(make-instance (cdr (assoc *default-sat-backend
*
42 *satwrap-backends
*))))
43 (:documentation
"A Sat solver abstraction"))
45 (defmethod sat-solver-numclauses ((solver sat-solver
))
46 (length (sat-solver-clauses solver
)))
48 (defmethod print-object ((solver sat-solver
) stream
)
49 (print-unreadable-object (solver stream
:type T
:identity T
)
50 (format stream
"~D vars, ~D clauses, backend ~A"
51 (sat-solver-numvars solver
)
52 (sat-solver-numclauses solver
)
53 (sat-solver-backend solver
))))
55 (defmethod clause-valid ((solver sat-solver
) (clause list
))
56 "Check that CLAUSE is a valid clause for SOLVER."
58 :with max
:= (sat-solver-numvars solver
)
61 :always
(and (not (zerop v
))
64 (defmacro iota
(n &optional
(start 1))
65 "Return a list of the N sequential integers starting at START (default: 1)."
66 (let ((i (gensym "i")))
71 (define-condition satwrap-condition
(error)
73 (:documentation
"Superclass of all conditions raised by satwrap code."))
75 (define-condition invalid-clause
(satwrap-condition)
76 ((solver :initarg
:solver
:reader invalid-clause-solver
)
77 (clause :initarg
:clause
:reader invalid-clause-clause
))
78 (:report
(lambda (condition stream
)
79 (format stream
"Invalid clause ~A for solver ~A"
80 (invalid-clause-clause condition
)
81 (invalid-clause-solver condition
)))))
83 (define-condition invalid-backend
(satwrap-condition)
84 ((name :initarg
:name
:reader invalid-backend-name
))
85 (:report
(lambda (condition stream
)
86 (declare (special *satwrap-backends
* *default-sat-backend
*))
87 (format stream
"Invalid backend ~S specified. Supported: ~{~S~^, ~}, default ~S."
88 (invalid-backend-name condition
)
89 (mapcar #'car
*satwrap-backends
*)
90 *default-sat-backend
*))))
92 (defmethod flush-to-backend ((solver sat-solver
))
93 "Populate backend, possibly flushing old backend contents."
94 (reinitialize-instance (sat-solver-backend solver
))
95 ;; declare proper number of variables
96 (setf (satwrap.backend
:numvars
(sat-solver-backend solver
))
97 (sat-solver-numvars solver
))
98 (dolist (c (sat-solver-clauses solver
))
99 (satwrap.backend
:add-clause
(sat-solver-backend solver
) c
)))
102 (defvar *default-sat-backend
* :precosat
103 "Name of the default backend to be used by make-sat-solver.")
105 (defparameter *satwrap-backends
*
106 `((:precosat .
,(find-class 'satwrap.precosat
:precosat-backend
)))
107 "Alist of symbolic name to backend class name for all supported backends.")
109 (defun make-sat-solver (&optional
(backend *default-sat-backend
*))
110 "Return a new sat solver instance. Optional argument BACKEND can be used to
111 specify which backend should be used. It defaults to *default-sat-backend*."
112 (let ((be (assoc backend
*satwrap-backends
*)))
114 (make-instance 'sat-solver
:backend
(make-instance (cdr be
)))
115 (error 'invalid-backend
:name backend
))))
117 (defgeneric add-variable
(solver)
118 (:documentation
"Add another variable to SOLVER. Returns new variable index.")
119 (:method
((solver sat-solver
))
120 (incf (sat-solver-numvars solver
))))
122 (defgeneric add-clause
(solver clause
)
123 (:documentation
"Add CLAUSE to SOLVER's cnf formula. Clause is consumed.")
124 (:method
((solver sat-solver
) (clause list
))
125 (if (clause-valid solver clause
)
126 (push clause
(sat-solver-clauses solver
))
127 (error 'invalid-clause
:clause clause
:solver solver
)))
128 (:method
((solver sat-solver
) (clause vector
))
129 (add-clause solver
(coerce clause
'list
))))
131 (defgeneric satisfiablep
(solver &key assume
)
132 (:documentation
"Check whether current CNF in SOLVER is satisfiable.
133 Keyword argument :ASSUME can provide a sequence of literals assumed TRUE or FALSE.
135 (:method
((solver sat-solver
) &key
(assume '()))
136 (if (clause-valid solver assume
) ;; misusing 'clause' concept here
138 (flush-to-backend solver
)
139 (satwrap.backend
:satisfiablep
(sat-solver-backend solver
) assume
))
140 (error 'invalid-clause
:clause assume
:solver solver
))))
142 (defgeneric solution
(solver &key interesting-vars
)
143 (:documentation
"Return solution for SOLVER. If unsat, return '(). If sat return
144 sequence of 0/1 values for variables [1...N]. Keyword argument INTERESTING-VARS can be used to restrict the variables whose values are reported. Solution components will be in the same order that INTERESTING-VARS lists the variables in.")
145 (:method
((solver sat-solver
)
146 &key
(interesting-vars (iota (sat-solver-numvars solver
))))
147 (satwrap.backend
:solution
(sat-solver-backend solver
) interesting-vars
)))