def _parse_ite(expr):
"""
This method takes in any expression EXPR and parses it into
a F, G, H expressions such that expr is the same as ite(F,G,H).
This is possible because every boolean function can be represented
in ite form. See Bryant's paper for formulas.
"""
if expr["type"] == "const":
v = expr["value"]
return pbb.mk_const_expr(v),pbb.mk_const_expr(v),pbb.mk_const_expr(v)
if expr["type"] == "var":
return expr, pbb.mk_const_expr(True), pbb.mk_const_expr(False)
if expr["type"] == "neg":
return expr["expr"], pbb.mk_const_expr(False), pbb.mk_const_expr(True)
if expr["type"] == "and":
return expr["expr1"], expr["expr2"], pbb.mk_const_expr(False)
if expr["type"] == "or":
return expr["expr1"], pbb.mk_const_expr(True), expr["expr2"]
if expr["type"] == "impl":
return expr["expr1"], expr["expr2"], pbb.mk_const_expr(True)
if expr["type"] == "xor":
return expr["expr1"], pbb.mk_neg_expr(expr["expr2"]), expr["expr2"]
if expr["type"] == "eqv":
return expr["expr1"], expr["expr2"], pbb.mk_neg_expr(expr["expr2"])
def _parse_ite(expr):
"""
This method takes in any expression EXPR and parses it into
a F, G, H expressions such that expr is the same as ite(F,G,H).
This is possible because every boolean function can be represented
in ite form. See Bryant's paper for formulas.
"""
if expr["type"] == "const":
v = expr["value"]
return pbb.mk_const_expr(v), pbb.mk_const_expr(v), pbb.mk_const_expr(v)
if expr["type"] == "var":
return expr, pbb.mk_const_expr(True), pbb.mk_const_expr(False)
if expr["type"] == "neg":
return expr["expr"], pbb.mk_const_expr(False), pbb.mk_const_expr(True)
if expr["type"] == "and":
return expr["expr1"], expr["expr2"], pbb.mk_const_expr(False)
if expr["type"] == "or":
return expr["expr1"], pbb.mk_const_expr(True), expr["expr2"]
if expr["type"] == "impl":
return expr["expr1"], expr["expr2"], pbb.mk_const_expr(True)
if expr["type"] == "xor":
return expr["expr1"], pbb.mk_neg_expr(expr["expr2"]), expr["expr2"]
if expr["type"] == "eqv":
return expr["expr1"], expr["expr2"], pbb.mk_neg_expr(expr["expr2"])
def simplify(expr):
"""
Tries to simplify expressions very niavely.
"""
expr = propagate(expr, (None, True))
if type(expr) == bool:
return PBB.mk_const_expr(expr)
return expr
def propagate(expr, tup):
"""
Propagae the assignment TUP (string variable name, boolean value)
through expression EXPR
"""
expr = PBA.propagate(expr, tup)
if type(expr) == bool:
return PBB.mk_const_expr(expr)
return expr
def simplify(expr):
expr = propagate(expr, (None, True))
if type(expr) == bool:
return PBB.mk_const_expr(expr)
return expr
