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Add tail calls to the interpreter #15

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Add tail calls to the interpreter #15

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182 changes: 98 additions & 84 deletions scrapscript.py
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Original file line number Diff line number Diff line change
Expand Up @@ -635,91 +635,105 @@ def match(obj: Object, pattern: Object) -> Optional[Env]:

# pylint: disable=redefined-builtin
def eval_exp(env: Env, exp: Object) -> Object:
logger.debug(exp)
if isinstance(exp, (Int, Bool, String, Bytes, Hole, Closure, NativeFunction)):
return exp
if isinstance(exp, Var):
value = env.get(exp.name)
if value is None:
raise NameError(f"name '{exp.name}' is not defined")
return value
if isinstance(exp, Binop):
handler = BINOP_HANDLERS.get(exp.op)
if handler is None:
raise NotImplementedError(f"no handler for {exp.op}")
return handler(env, exp.left, exp.right)
if isinstance(exp, List):
return List([eval_exp(env, item) for item in exp.items])
if isinstance(exp, Record):
return Record({k: eval_exp(env, exp.data[k]) for k in exp.data})
if isinstance(exp, Assign):
# TODO(max): Rework this. There's something about matching that we need
# to figure out and implement.
assert isinstance(exp.name, Var)
value = eval_exp(env, exp.value)
return EnvObject({**env, exp.name.name: value})
if isinstance(exp, Where):
res_env = eval_exp(env, exp.binding)
assert isinstance(res_env, EnvObject)
new_env = {**env, **res_env.env}
return eval_exp(new_env, exp.body)
if isinstance(exp, Assert):
cond = eval_exp(env, exp.cond)
if cond != Bool(True):
raise AssertionError(f"condition {exp.cond} failed")
return eval_exp(env, exp.value)
if isinstance(exp, Function):
if not isinstance(exp.arg, Var):
raise RuntimeError(f"expected variable in function definition {exp.arg}")
return Closure(env, exp)
if isinstance(exp, MatchFunction):
return Closure(env, exp)
if isinstance(exp, Apply):
if isinstance(exp.func, Var) and exp.func.name == "$$quote":
return exp.arg
callee = eval_exp(env, exp.func)
if isinstance(callee, NativeFunction):
arg = eval_exp(env, exp.arg)
return callee.func(arg)
if not isinstance(callee, Closure):
raise TypeError(f"attempted to apply a non-closure of type {type(callee).__name__}")
arg = eval_exp(env, exp.arg)
if isinstance(callee.func, Function):
assert isinstance(callee.func.arg, Var)
new_env = {**callee.env, callee.func.arg.name: arg}
return eval_exp(new_env, callee.func.body)
elif isinstance(callee.func, MatchFunction):
# TODO(max): Implement MatchClosure
while True:
logger.debug(exp)
if isinstance(exp, (Int, Bool, String, Bytes, Hole, Closure, NativeFunction)):
return exp
if isinstance(exp, Var):
value = env.get(exp.name)
if value is None:
raise NameError(f"name '{exp.name}' is not defined")
return value
if isinstance(exp, Binop):
# TODO(max): Inline these to avoid recursion
handler = BINOP_HANDLERS.get(exp.op)
if handler is None:
raise NotImplementedError(f"no handler for {exp.op}")
return handler(env, exp.left, exp.right)
if isinstance(exp, List):
# TODO(max): Remove recursion
return List([eval_exp(env, item) for item in exp.items])
if isinstance(exp, Record):
# TODO(max): Remove recursion
return Record({k: eval_exp(env, exp.data[k]) for k in exp.data})
if isinstance(exp, Assign):
# TODO(max): Rework this. There's something about matching that we need
# to figure out and implement.
assert isinstance(exp.name, Var)
# TODO(max): Remove recursion
value = eval_exp(env, exp.value)
return EnvObject({**env, exp.name.name: value})
if isinstance(exp, Where):
res_env = eval_exp(env, exp.binding)
assert isinstance(res_env, EnvObject)
new_env = {**env, **res_env.env}
env = new_env
exp = exp.body
continue
if isinstance(exp, Assert):
cond = eval_exp(env, exp.cond)
if cond != Bool(True):
raise AssertionError(f"condition {exp.cond} failed")
exp = exp.value
continue
if isinstance(exp, Function):
if not isinstance(exp.arg, Var):
raise RuntimeError(f"expected variable in function definition {exp.arg}")
return Closure(env, exp)
if isinstance(exp, MatchFunction):
return Closure(env, exp)
if isinstance(exp, Apply):
if isinstance(exp.func, Var) and exp.func.name == "$$quote":
return exp.arg
callee = eval_exp(env, exp.func)
if isinstance(callee, NativeFunction):
arg = eval_exp(env, exp.arg)
return callee.func(arg)
if not isinstance(callee, Closure):
raise TypeError(f"attempted to apply a non-closure of type {type(callee).__name__}")
arg = eval_exp(env, exp.arg)
for case in callee.func.cases:
m = match(arg, case.pattern)
if m is None:
continue
return eval_exp({**env, **m}, case.body)
raise MatchError("no matching cases")
else:
raise TypeError(f"attempted to apply a non-function of type {type(callee.func).__name__}")
if isinstance(exp, Access):
obj = eval_exp(env, exp.obj)
if isinstance(obj, Record):
if not isinstance(exp.at, Var):
raise TypeError(f"cannot access record field using {type(exp.at).__name__}, expected a field name")
if exp.at.name not in obj.data:
raise NameError(f"no assignment to {exp.at.name} found in record")
return obj.data[exp.at.name]
elif isinstance(obj, List):
access_at = eval_exp(env, exp.at)
if not isinstance(access_at, Int):
raise TypeError(f"cannot index into list using type {type(access_at).__name__}, expected integer")
if access_at.value < 0 or access_at.value >= len(obj.items):
raise ValueError(f"index {access_at.value} out of bounds for list")
return obj.items[access_at.value]
raise TypeError(f"attempted to access from type {type(obj).__name__}")
if isinstance(exp, Compose):
clo_inner = eval_exp(env, exp.inner)
clo_outer = eval_exp(env, exp.outer)
return Closure({}, Function(Var("x"), Apply(clo_outer, Apply(clo_inner, Var("x")))))
raise NotImplementedError(f"eval_exp not implemented for {exp}")
if isinstance(callee.func, Function):
assert isinstance(callee.func.arg, Var)
new_env = {**callee.env, callee.func.arg.name: arg}
env = new_env
exp = callee.func.body
continue
elif isinstance(callee.func, MatchFunction):
# TODO(max): Implement MatchClosure
arg = eval_exp(env, exp.arg)
for case in callee.func.cases:
m = match(arg, case.pattern)
if m is None:
continue
env = {**env, **m}
exp = case.body
break
else:
raise MatchError("no matching cases")
continue
else:
raise TypeError(f"attempted to apply a non-function of type {type(callee.func).__name__}")
if isinstance(exp, Access):
obj = eval_exp(env, exp.obj)
if isinstance(obj, Record):
if not isinstance(exp.at, Var):
raise TypeError(f"cannot access record field using {type(exp.at).__name__}, expected a field name")
if exp.at.name not in obj.data:
raise NameError(f"no assignment to {exp.at.name} found in record")
return obj.data[exp.at.name]
elif isinstance(obj, List):
access_at = eval_exp(env, exp.at)
if not isinstance(access_at, Int):
raise TypeError(f"cannot index into list using type {type(access_at).__name__}, expected integer")
if access_at.value < 0 or access_at.value >= len(obj.items):
raise ValueError(f"index {access_at.value} out of bounds for list")
return obj.items[access_at.value]
raise TypeError(f"attempted to access from type {type(obj).__name__}")
if isinstance(exp, Compose):
clo_inner = eval_exp(env, exp.inner)
clo_outer = eval_exp(env, exp.outer)
return Closure({}, Function(Var("x"), Apply(clo_outer, Apply(clo_inner, Var("x")))))
raise NotImplementedError(f"eval_exp not implemented for {exp}")


def bencode(obj: object) -> bytes:
Expand Down