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]
