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Microkanren tryout.
import itertools
# Microkanren programs are 'goal' functions that take in a
# state and return a stream of states that satisfy the given goal.
# I am interested about microkanren because it presents a logic
# programming kernel which fits into a dynamically typed language.
# Anything could go as a variable, but I wanted names for variables.
class Variable(object):
def __init__(self, name=''):
self.name = name
def __repr__(self):
return self.name or '<{}>'.format(id(self))
# State consists of unification results, it can be simple such as an assoc list.
def load(st, var):
if isinstance(var, Variable):
for key, value in reversed(st):
if key is var:
if isinstance(value, Variable):
return load(st, value)
return value
return var
# Equality, conjunction and disjunction are goal constructors..
def eq(a_, b_):
def _impl_(st):
a = load(st, a_)
b = load(st, b_)
if a is b: # not want to grow state with (a, a) -associations.
yield st
elif isinstance(a, Variable):
yield st + [(a, b)] # The only place where state can grow.
elif isinstance(b, Variable):
yield st + [(b, a)]
elif isinstance(a, tuple) and isinstance(b, tuple) and len(a) == len(b) > 0:
for fn in reduce(conj, [eq(x, y) for x, y in zip(a, b)]):
for st in fn(st): # Tuple unification treated as: (a,b)=(b,c) -> {a=b, b=c}
yield st
elif a == b:
yield st
return _impl_
# Conj is bit like AND and Disj bit like OR.
def conj(x, y):
def _impl_(st):
for st in x(st):
for st in y(st):
yield st
return _impl_
def disj(x, y):
def _impl_(st):
xs = x(st)
ys = y(st)
for xst, yst in itertools.izip(xs, ys):
yield xst
yield yst
for xst in xs:
yield xst
for yst in ys:
yield yst
return _impl_
# Say I'd like to write an assembler using microkanren..
def cat(oktet_, e_, f_):
def _impl_(st):
oktet = load(st, oktet_)
e = load(st, e_)
f = load(st, f_)
if isinstance(f, str):
return conj(eq(oktet, ord(f[0])), eq(e, f[1:]))(st)
elif isinstance(e, str) and isinstance(oktet, int):
return eq(chr(oktet) + e, f)(st)
return iter(())
return _impl_
def byt(oktet):
def _impl(e, f):
return cat(oktet, e, f)
return _impl
def pat(*patterns):
def _impl_(e, f):
goals = []
for pattern in reversed(patterns):
t = Variable()
goals.append(pattern(t, f))
f = t
goals.append(eq(e, f))
return reduce(conj, reversed(goals))
return _impl_
if __name__=='__main__':
a = ""
b = Variable('b')
c = Variable('c')
k = Variable('k')
goal = pat(byt(k), byt(124), byt(125))(a, b)
goal = conj(disj(
eq(k, 124),
eq(k, 125),
), conj(goal, disj(
conj(eq(k, 124), byt(5)(b, c)),
conj(eq(k, 125), byt(6)(b, c)),
)))
for st in goal([]):
print st
print 'test'
# ..hmm. This is not sufficient.
oktet = Variable('oktet')
postfix = Variable('postfix')
for st in cat(oktet, postfix, "xyz")([]):
print st
for st in cat(ord("x"), "yz", "xyz")([]):
print st
for st in cat(oktet, "yz", "xyz")([]):
print st
midfix = Variable('midfix')
for st in conj(eq(oktet, ord("x")), conj(cat(oktet, "yz", midfix), cat(oktet, midfix, postfix)))([]):
print st
x = Variable('x')
y = Variable('y')
z = Variable('z')
for st in conj(eq(x, 5), disj(eq(x, y), eq(x, z)))([]):
print st
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