def eval_let(self, expr, env):
extended_env = env.extended()
for decl in expr.declarations:
if not decl.is_definition(): continue
extended_env.define(decl.lhs.name,
values.Thunk(decl.rhs, extended_env))
yield from self.eval_expression(expr.body, extended_env)
def unify(self, goals):
if not goals:
yield values.unit()
return
(value1, value2) = goals[0]
goals = goals[1:]
if not value1.is_decided():
for v1 in self.eval_value(value1):
yield from self.unify([(v1, value2)] + goals)
return
elif not value2.is_decided():
for v2 in self.eval_value(value2):
yield from self.unify([(value1, v2)] + goals)
return
if value1.is_integer_constant() and value2.is_integer_constant():
if value1.value == value2.value: yield from self.unify(goals)
elif value1.is_rigid_structure() and value2.is_rigid_structure():
if value1.constructor == value2.constructor and \
len(value1.args) == len(value2.args):
subgoals = list(zip(value1.args, value2.args))
yield from self.unify(subgoals + goals)
# Same head:
# x t1 ... tn == x s1 ... sn
#elif val1.is_flex_structure() \
# and val2.is_flex_structure() \
# and val1.symbol == val2.symbol \
# and len(val1.args) == len(val2.args):
# subgoals = list(zip(val1.args, val2.args))
# yield from self.unify(subgoals + goals)
elif value1.is_flex_structure() and len(value1.args) == 0:
# TODO: occurs check
assert not value1.symbol.is_instantiated() # decided
value1.symbol.instantiate(value2)
yield from self.unify(goals)
value1.symbol.uninstantiate()
elif value1.is_flex_structure() and len(value1.args) > 0:
# TODO: occurs check
assert not value1.symbol.is_instantiated() # decided
new_var = syntax.fresh_variable()
params = [syntax.fresh_variable() for arg in value1.args]
term = syntax.lambda_many(
[p.name for p in params],
syntax.alternative(
syntax.sequence_many1(
[
syntax.unify(p, a)
for p, a in zip(params, value1.args)
],
value2 # body
),
syntax.application_many(new_var, params)))
env = environment.PersistentEnvironment()
env.define(new_var.name,
values.FlexStructure(values.Metavar(prefix='F'), []))
value1.symbol.instantiate(values.Thunk(term, env))
yield from self.unify(goals)
value1.symbol.uninstantiate()
elif value2.is_flex_structure():
yield from self.unify([(value2, value1)] + goals)
else:
return # Otherwise we fail
def eval_application(self, expr, env):
for value in self.eval_expression(expr.fun, env):
yield from self.apply(value, values.Thunk(expr.arg, env))
def unify(self, goals):
if len(goals) == 0:
yield values.unit()
return
(val1, val2) = goals[0]
goals = goals[1:]
if not val1.is_decided():
for v1 in self.eval_value(val1):
yield from self.unify([(v1, val2)] + goals)
return
elif not val2.is_decided():
for v2 in self.eval_value(val2):
yield from self.unify([(val1, v2)] + goals)
return
if val1.is_integer_constant() and val2.is_integer_constant():
if val1.value == val2.value:
yield from self.unify(goals)
elif val1.is_rigid_structure() and val2.is_rigid_structure():
if val1.constructor == val2.constructor and \
len(val1.args) == len(val2.args):
subgoals = list(zip(val1.args, val2.args))
yield from self.unify(subgoals + goals)
# Same head:
# x t1 ... tn == x s1 ... sn
elif val1.is_flex_structure() \
and val2.is_flex_structure() \
and val1.symbol == val2.symbol \
and len(val1.args) == len(val2.args):
subgoals = list(zip(val1.args, val2.args))
yield from self.unify(subgoals + goals)
elif val1.is_flex_structure() and len(val1.args) == 0:
# TODO: occurs check
assert not val1.symbol.is_instantiated() # decided
val1.symbol.instantiate(val2)
yield from self.unify(goals)
val1.symbol.uninstantiate()
elif val1.is_flex_structure() and len(val1.args) > 0:
# TODO: occurs check
assert not val1.symbol.is_instantiated() # decided
new_var = syntax.fresh_variable()
params = []
u_goals = []
for arg in val1.args:
param = syntax.fresh_variable()
params.append(param)
u_goals.append(syntax.unify(param, arg))
term = syntax.lambda_many(
[p.name for p in params],
syntax.alternative(
syntax.sequence_many1(
u_goals,
val2 # body
),
syntax.application_many(new_var, params)))
env = environment.PersistentEnvironment()
env.define(new_var.name,
values.FlexStructure(values.Metavar(prefix='F'), []))
val1.symbol.instantiate(values.Thunk(term, env))
yield from self.unify(goals)
val1.symbol.uninstantiate()
elif val2.is_flex_structure():
yield from self.unify([(val2, val1)] + goals)
elif val1.is_closure():
#print('OPEN')
#print(val1.var)
#print(val1.body)
#print(val1.env)
uvar = values.UniversalVariable(prefix=val1.var)
uval = values.UniversalStructure(uvar, [])
env1 = val1.env.extended()
env2 = environment.PersistentEnvironment()
env1.define(val1.var, uval)
env2.define(val1.var, uval)
lhs = values.Thunk(val1.body, env1)
rhs = values.Thunk(syntax.Application(fun=val2, arg=uval), env2)
for x in self.unify([(lhs, rhs)]):
# TODO:
# forbid metavariables pointing directly
# or indirectly to uvar
# (???)
yield from self.unify(goals)
elif val2.is_closure():
yield from self.unify([(val2, val1)] + goals)
else:
print(val1, val2)
return # Otherwise we fail