def find_instance(self, mono):
'''find typeclass instance matching mono'''
tool.debug('finding instance of:', self.name, mono.show())
# print('finding instance of:', self.name, 'for:', mono.show())
t = type(mono)
matches = []
for scheme, instance in self.instances.items():
# TODO what about depth ?
fresh = hm.instantiate( scheme )
try:
# note: we unify in a fresh union_find
hm.unify(tool.UnionFind(), fresh, mono)
matches.append( (scheme, instance) )
except error.Type:
pass
if not matches:
raise error.Type('typeclass {0} has no instance for type {1}'
.format( self.name, mono.show() ))
if len(matches) > 1:
raise error.Type('ambiguous {0} instances for {1}'.format(self.name, mono.show()))
return matches[0]
def unify(uf, a, b):
a = uf.find(a)
b = uf.find(b)
ta = type(a)
tb = type(b)
# sa, sb = hm.show(a, b)
# print('typeclass unify', a.show(), 'with:', b.show() )
assert ta is Var or tb is Var
if ta is Var and tb is Var:
# create a fresh constrained variable with constraint union
depth = min(a.depth, b.depth)
c = Var(depth, a.context | b.context )
# and link both
uf.link(a, c)
uf.link(b, c)
return
var = a if ta is Var else b
other = a if tb is Var else b
if type(other) is hm.Var:
# constrained variable becomes representant
uf.link(other, var)
return
# check instances
for tc in var.context:
# find a type scheme that matches 'other' in the
# instances for this type constructor
scheme, instance = tc.find_instance( other.nice(uf) )
# context reduction happens here: we instantiate the
# type scheme (possibly containing bounded variables)
# and unify with other
# propagate further constraints, if any
if any( type(b) is Var for b in scheme.bound ):
# TODO what about the depth when instantiating scheme ?
hm.unify(uf, hm.instantiate(scheme), other)
# we made it so far, we may link now
uf.link(var, other)
return
def find_overload(self, identifier, mono):
tool.debug('finding overload for:', identifier, ':', mono.show())
proto = self.definition[identifier]
uf = tool.UnionFind()
fresh = hm.instantiate(hm.generalize(proto))
vars = fresh.variables()
assert len(vars) == 1
hm.unify(uf, fresh, mono)
a = next(iter(vars))
t = uf.find( a )
scheme, instance = self.find_instance(t)
return instance[identifier]
def unify(uf, a, b):
"""unify row types ra and rb"""
a = uf.find(a)
b = uf.find(b)
ta = type(a)
tb = type(b)
assert ta in types and tb in types
# print( ra, rb)
if ta is Extension and tb is Extension:
if a.label == b.label:
# unify heads
hm.unify(uf, a.mono, b.mono)
# unify tails
unify(uf, a.tail, b.tail)
else:
try:
# try pulling b's head in a
tool.debug("pulling", b.label)
pa = a.pull(b.label)
unify(uf, pa, b)
# it worked: remember pa is originially a
uf.link(pa, a)
except PullError:
try:
# try pulling a's head in b
tool.debug("pulling", a.label)
pb = b.pull(a.label)
unify(uf, a, pb)
# it worked: remember pa is originially b
uf.link(pb, b)
except PullError:
tool.debug("union")
# none of it worked: neither heads is present in
# other type. try to unify both to record union
# unify a's tail var with a fresh copy of b
try:
unify(uf, a.var(), b.fresh())
unify(uf, b.var(), a.fresh())
except FreshError:
sa, sb = hm.show(a, b)
raise error.Type("can not unify row type {0} with {1}".format(sa, sb))
elif ta is Var or tb is Var:
var = a if ta is Var else b
other = a if tb is Var else b
uf.link(var, other)
# tool.debug('repr:', other.show())
elif a != b:
raise error.Type("can not unify row type {0} with {1}".format(a.show(), b.show()))
else:
assert ta is Empty and tb is Empty
