def let(se: SExpression, stg: LexicalVarStorage) -> SExpression:
"""
The ``let`` macro binds variables to a local scope: the expressions
inside the macro. Like a function, a ``let`` returns the last
expression in its body. Once the ``let`` returns, the variables are
unbound, and cannot be accessed anymore. For example::
(let ((a (+ f g))
(b 11)
(c 12))
(+ a (- b c)))
In the example above, ``a`` was bound to whatever ``(+ f g)``
evaluates to, b to ``11``, and ``c`` to ``12``.
Notice how the above was equivalent to another expression::
((lambda (a b c)
(+ a (- b c))) (+ f g) 11 12)
You should do a syntax translation from the input to something like that.
>>> from slyther.types import *
>>> from slyther.parser import lisp
>>> from slyther.evaluator import lisp_eval
>>> stg = LexicalVarStorage(
... {'let': Variable(let),
... 'lambda': Variable(lambda_func),
... 'print': Variable(print_),
... 'x': Variable(10)})
>>> lisp_eval(lisp('(let ((x 20) (y 30)) (print x) (print y))'), stg)
20
30
NIL
>>> lisp_eval(Symbol('x'), stg)
10
"""
new_environ = {**stg.environ}
new_local = {**stg.local}
new_lex_var = LexicalVarStorage(new_environ)
new_lex_var.local = new_local
for item in se.car:
new_lex_var.put(item.car, lisp_eval(item.cdr.car, stg))
return_val = NIL
for item in se.cdr:
return_val = lisp_eval(item, new_lex_var)
return return_val
def setbang(se: SExpression, stg: LexicalVarStorage):
"""
``set!`` is the assigment macro. Unlike ``define``, ``set!`` **does not
create new variables.** Instead, it changes the value of existing
variables **only**. If given a variable which has not been defined,
it should raise a ``KeyError``.
For example::
(set! <name> <value>)
Should just eval ``value`` and call ``stg[name].set`` on it. Return
``NIL``.
>>> from slyther.types import *
>>> from slyther.parser import lisp
>>> stg = LexicalVarStorage({'foo': Variable(12), 'bar': Variable(15)})
>>> old_foo = stg['foo']
>>> setbang(lisp('(foo 15)'), stg)
NIL
>>> stg['foo'].value
15
>>> stg['foo'] is old_foo
True
>>> setbang(lisp('(baz 15)'), stg)
Traceback (most recent call last):
...
KeyError: 'Undefined variable baz'
"""
try:
stg[se.car].set(lisp_eval(se.cdr.car, stg))
return NIL
except KeyError as ex:
raise KeyError("Undefined variable {}".format(str(se.car))) from ex
def if_expr(se: SExpression, stg: LexicalVarStorage):
"""
An ``if`` expression looks like this::
(if <predicate> <consequent> <alternative>)
If the predicate evaluates to something truthy, return the
consequent, otherwise return the alternative. An example::
(if (< x 10)
(print "x is less than 10")
(print "x is greater than or equal to 10"))
>>> from slyther.types import *
>>> from slyther.parser import lisp
>>> se = lisp('((< x 10)'
... ' (print "x is less than 10")'
... ' (print "x is greater than or equal to 10"))')
>>> stg = LexicalVarStorage({})
>>> stg.put('<', lt)
>>> stg.put('x', 9)
>>> if_expr(se, stg)
(print "x is less than 10")
>>> stg['x'].set(10)
>>> if_expr(se, stg)
(print "x is greater than or equal to 10")
"""
if lisp_eval(se.car, stg):
return se.cdr.car
else:
return se.cdr.cdr.car
def __call__(self, *args):
"""
Call the function with arguments ``args``.
Make use of ``lisp_eval``. Note that a fully working ``lisp_eval``
implementation will require this function to work properly, and this
will require a working ``lisp_eval`` to work properly, so you must
write both before you can test it.
Warning: Do not make any attempt to modify ``environ`` here. That is
not how lexical scoping works. Instead, construct a new
``LexicalVarStorage`` from the existing environ.
"""
# avoid circular imports
from slyther.evaluator import lisp_eval
storage = LexicalVarStorage(self.environ)
for x, y in zip(args, self.params):
storage.put(y, x)
r = NIL
length = len(self.body)
for index, z in enumerate(self.body):
if index == length - 1:
return (z, storage)
else:
r = lisp_eval(z, storage)
return r
def define(se: SExpression, stg: LexicalVarStorage):
"""
Define a variable or a function to a value, calling ``put`` on
the storage::
; variable
(define var-name evaluate-me)
; lambda function
(define func-name (lambda (args...) (body1) ... (bodyN)))
; SE-named function
(define (func-name args...) (body1) ... (bodyN))
.. note::
If defining a function (either by ``lambda`` or by SE-named
syntax), the definition **must** be made visible from within
that function's ``environ``, or recursion will not work!
>>> from slyther.types import *
>>> from slyther.parser import lisp
>>> se = lisp('((twirl alpha beta) (print alpha) (print beta))')
>>> name = Symbol('twirl')
>>> args = lisp('(alpha beta)')
>>> body = lisp('((print alpha) (print beta))')
>>> stg = LexicalVarStorage({})
>>> stg.put('NIL', NIL)
>>> stg.put('define', define)
>>> stg.put('lambda', lambda_func)
>>> from slyther.evaluator import lisp_eval
>>> lisp_eval(define(cons(cons(name, args), body), stg), stg)
NIL
>>> lisp_eval(define(lisp('(x 10)'), stg), stg)
NIL
>>> stg[name].value
(lambda (alpha beta) (print alpha) (print beta))
>>> stg[name].value.environ['twirl'].value
(lambda (alpha beta) (print alpha) (print beta))
>>> stg['x'].value
10
>>> stg[name].value.environ['x'].value
Traceback (most recent call last):
...
KeyError: 'x'
"""
key = se.car
value = se.cdr
if isinstance(key, SExpression):
function = UserFunction(params=key.cdr, body=value, environ=stg.fork())
key = key.car
function.environ[key] = Variable(function)
stg.put(key, function)
elif isinstance(key, Symbol):
stg.put(key, lisp_eval(value.car, stg))
else:
stg.put(key, value)
def eval(self, expr):
"""
Eval a single (parsed) lisp expression.
"""
try:
return lisp_eval(expr, self.stg)
except RecursionError as e:
raise RecursionError(
"Maximum recursion depth exceeded while evaluating {!r}"
.format(expr)) from e
def and_(se: SExpression, stg: LexicalVarStorage):
"""
Compute an ``and`` expression, like this::
(and (< x 10) (> y 15) (foo? z))
Evaluate left to right, and return the first result which produces
a falsy value. Note that the result need not be a boolean, but you
should test its falsiness(parse(lex('''
... (cond
... ((< x 5) (print "x < 5"))
... ((< x 10) (print "5 <= x < 10"))
... ((< x 15) (print "10 <= x < 15"))
... (#t (print "x >= 15")))'''))), and return the result (even if it's not
a boolean).
Note that you could return the last expression unevaluated if all
the previous are truthy, as your ``lisp_eval`` should eval it for
you. This could be useful for tail call optimization.
>>> from slyther.types import *
>>> from slyther.parser import lisp
>>> from slyther.evaluator import lisp_eval
>>> stg = LexicalVarStorage(
... {'and': Variable(and_),
... '#f': Variable(Boolean(False)),
... '#t': Variable(Boolean(True)),
... 'print': Variable(print_),
... '+': Variable(add),
... 'x': Variable(0),
... 'y': Variable(1),
... 'z': Variable(2)})
>>> lisp_eval(lisp('(and #t (print (+ x y z)) #f)'), stg)
3
NIL
>>> lisp_eval(lisp('(and #f (print (+ x y z)) #f)'), stg)
#f
>>> lisp_eval(lisp('(and #t x (print (+ x y z)) y foo)'), stg)
0
>>> lisp_eval(lisp('(and (+ x y) y z)'), stg)
2
>>> lisp_eval(lisp('(and)'), stg)
NIL
"""
res = NIL
length = len(se)
for index, x in enumerate(se):
if index == length - 1:
return x
y = lisp_eval(x, stg)
res = y
if not y:
return y
return res
def and_(se: SExpression, stg: LexicalVarStorage):
"""
Compute an ``and`` expression, like this::
(and (< x 10) (> y 15) (foo? z))
Evaluate left to right, and return the first result which produces
a falsy value. Note that the result need not be a boolean, but you
should test its falsiness, and return the result (even if it's not
a boolean).
Note that you could return the last expression unevaluated if all
the previous are truthy, as your ``lisp_eval`` should eval it for
you. This could be useful for tail call optimization.
>>> from slyther.types import *
>>> from slyther.parser import lisp
>>> from slyther.evaluator import lisp_eval
>>> stg = LexicalVarStorage(
... {'and': Variable(and_),
... '#f': Variable(Boolean(False)),
... '#t': Variable(Boolean(True)),
... 'print': Variable(print_),
... '+': Variable(add),
... 'x': Variable(0),
... 'y': Variable(1),
... 'z': Variable(2)})
>>> lisp_eval(lisp('(and #t (print (+ x y z)) #f)'), stg)
3
NIL
>>> lisp_eval(lisp('(and #f (print (+ x y z)) #f)'), stg)
#f
>>> lisp_eval(lisp('(and #t x (print (+ x y z)) y foo)'), stg)
0
>>> lisp_eval(lisp('(and (+ x y) y z)'), stg)
2
>>> lisp_eval(lisp('(and)'), stg)
NIL
"""
'''
if(se.car is NIL):
return NIL
'''
return_val = NIL
for item in se.cells():
if item.cdr is not NIL:
return_val = lisp_eval(item.car, stg)
else:
return item.car
if not return_val:
return return_val
return return_val
'''
def test_function_return():
environ = stg.fork()
func = UserFunction(params=lisp('(a b)'),
body=lisp('''((collect 'add-result (add a b))
(add a b))'''),
environ=environ.copy())
assert environ == func.environ
stg.put('func', func)
result = lisp_eval(lisp('(func 10 50)'), stg)
# If this fails, then calling the function modified it's environ
# dictionary. This should NEVER happen.
assert environ == func.environ
assert collected['add-result'] == 60
assert result == 60
def eval_(se: SExpression, stg: LexicalVarStorage):
"""
::
(eval <expr>)
Evaluate ``expr``, if it produces a ``ConsList``, then upgrade that
``ConsList`` to an ``SExpression`` (recursively) and return it. Your
``lisp_eval`` will take care of actually evaluating the expression,
as this is a macro.
>>> from slyther.types import *
>>> from slyther.parser import lisp
>>> from slyther.evaluator import lisp_eval
>>> stg = LexicalVarStorage(
... {'eval': Variable(eval_),
... '#t': Variable(Boolean(True)),
... 'print': Variable(print_),
... 'x': Variable(0),
... 'y': Variable(1),
... 'z': Variable(lisp("(print x)"))})
>>> lisp_eval(lisp("(eval '(print x))"), stg)
0
NIL
>>> lisp_eval(lisp("(eval ''(print x))"), stg)
(list print x)
>>> lisp_eval(lisp('(eval #t)'), stg)
#t
>>> lisp_eval(lisp("(eval '''#t)"), stg)
'#t
>>> lisp_eval(lisp("(eval 'y)"), stg)
1
>>> lisp_eval(lisp("(eval ''y)"), stg)
y
>>> lisp_eval(lisp("(eval z)"), stg)
0
NIL
"""
expression = lisp_eval(se.car, stg)
if isinstance(expression, ConsList):
expression = SExpression.from_iterable(
eval_(SExpression(x), stg) for x in expression)
return expression
def or_(se: SExpression, stg: LexicalVarStorage):
"""
Similar to ``and`` above, but compute an ``or`` instead. Return
the first truthy value rather than falsy.
>>> from slyther.types import *
>>> from slyther.parser import lisp
>>> from slyther.evaluator import lisp_eval
>>> stg = LexicalVarStorage(
... {'or': Variable(or_),
... '#f': Variable(Boolean(False)),
... '#t': Variable(Boolean(True)),
... 'print': Variable(print_),
... '+': Variable(add),
... 'x': Variable(0),
... 'y': Variable(1),
... 'z': Variable(2)})
>>> lisp_eval(lisp('(or #t (print (+ x y z)) #f)'), stg)
#t
>>> lisp_eval(lisp('(or #f (print (+ x y z)) #f)'), stg)
3
#f
>>> lisp_eval(lisp('(or #f x (print (+ x y z)) y foo)'), stg)
3
1
>>> lisp_eval(lisp('(or (+ y -1) x z)'), stg)
2
>>> lisp_eval(lisp('(or)'), stg)
NIL
"""
'''
if(se.car is NIL):
return NIL
'''
return_val = NIL
for item in se.cells():
if item.cdr is not NIL:
return_val = lisp_eval(item.car, stg)
else:
return item.car
if return_val:
return return_val
return return_val
'''
def or_(se: SExpression, stg: LexicalVarStorage):
"""
Similar to ``and`` above, but compute an ``or`` instead. Return
the first truthy value rather than falsy.
>>> from slyther.types import *
>>> from slyther.parser import lisp
>>> from slyther.evaluator import lisp_eval
>>> stg = LexicalVarStorage(
... {'or': Variable(or_),
... '#f': Variable(Boolean(False)),
... '#t': Variable(Boolean(True)),
... 'print': Variable(print_),
... '+': Variable(add),
... 'x': Variable(0),
... 'y': Variable(1),
... 'z': Variable(2)})
>>> lisp_eval(lisp('(or #t (print (+ x y z)) #f)'), stg)
#t
>>> lisp_eval(lisp('(or #f (print (+ x y z)) #f)'), stg)
3
#f
>>> lisp_eval(lisp('(or #f x (print (+ x y z)) y foo)'), stg)
3
1
>>> lisp_eval(lisp('(or (+ y -1) x z)'), stg)
2
>>> lisp_eval(lisp('(or)'), stg)
NIL
"""
res = NIL
length = len(se)
for index, x in enumerate(se):
if index == length - 1:
return x
y = lisp_eval(x, stg)
res = y
if y:
return y
return res
def cond(se: SExpression, stg: LexicalVarStorage):
"""
``cond`` is similar to ``if``, but it lists a series of predicates
and consequents, similar to how guards work in Haskell. For
example::
(cond
((< x 5) (print "x < 5"))
((< x 10) (print "5 <= x < 10"))
((< x 15) (print "10 <= x < 15"))
(#t (print "x >= 15")))
>>> from slyther.types import *
>>> from slyther.parser import lex, parse
>>> def test_cond(x):
... expr = next(parse(lex('''
... (cond
... ((< x 5) (print "x < 5"))
... ((< x 10) (print "5 <= x < 10"))
... ((< x 15) (print "10 <= x < 15"))
... (#t (print "x >= 15")))''')))
... stg = LexicalVarStorage({})
... stg.put('<', lt)
... stg.put('#t', Boolean(True))
... stg.put('x', x)
... return cond(expr.cdr, stg)
>>> test_cond(4)
(print "x < 5")
>>> test_cond(5)
(print "5 <= x < 10")
>>> test_cond(10)
(print "10 <= x < 15")
>>> test_cond(15)
(print "x >= 15")
"""
while se is not NIL:
if (lisp_eval(se.car.car, stg)):
return se.car.cdr.car
se = se.cdr
def __call__(self, *args):
"""
Call the function with arguments ``args``.
Make use of ``lisp_eval``. Note that a fully working ``lisp_eval``
implementation will require this function to work properly, and this
will require a working ``lisp_eval`` to work properly, so you must
write both before you can test it.
Warning: Do not make any attempt to modify ``environ`` here. That is
not how lexical scoping works. Instead, construct a new
``LexicalVarStorage`` from the existing environ.
"""
# avoid circular imports
from slyther.evaluator import lisp_eval
new_lex_var = LexicalVarStorage(self.environ)
param_list = []
for item in self.params:
param_list.append(item)
# keyword argument handling code start
param_dict = {}
count = 0
for item in param_list:
param_dict[item] = count
count = count + 1
new_args = [0 for i in range(len(param_list))]
found_keyword_args = False
for index, item in enumerate(args):
s = str(item)
if ('=' in s):
equal_index = index_of_equal_sign(s)
new_args[param_dict[s[:equal_index]]] = int(s[equal_index +
1:])
found_keyword_args = True
else:
if (found_keyword_args):
raise BaseException(
'positional argument follows keyword argument')
new_args[index] = item
if (found_keyword_args):
args = new_args
# key word argument handling done
for p, a in zip(param_list, args):
new_lex_var.put(p, a)
for cell in self.body.cells():
if isinstance(cell.cdr, NilType):
return (cell.car, new_lex_var)
lisp_eval(cell.car, new_lex_var)
return NIL
def define(se: SExpression, stg: LexicalVarStorage):
"""
Define a variable or a function to a value, calling ``put`` on
the storage::
; variable
(define var-name evaluate-me)
; lambda function
(define func-name (lambda (args...) (body1) ... (bodyN)))
; SE-named function
(define (func-name args...) (body1) ... (bodyN))
.. note::
If defining a function (either by ``lambda`` or by SE-named
syntax), the definition **must** be made visible from within
that function's ``environ``, or recursion will not work!
>>> from slyther.types import *
>>> from slyther.parser import lisp
>>> se = lisp('((twirl alpha beta) (print alpha) (print beta))')
>>> name = Symbol('twirl')
>>> args = lisp('(alpha beta)')
>>> body = lisp('((print alpha) (print beta))')
>>> stg = LexicalVarStorage({})
>>> stg.put('NIL', NIL)
>>> stg.put('define', define) # so that you can return a define if you want
>>> stg.put('lambda', lambda_func)
>>> from slyther.evaluator import lisp_eval
>>> lisp_eval(define(cons(cons(name, args), body), stg), stg)
NIL
>>> lisp_eval(define(lisp('(x 10)'), stg), stg)
NIL
>>> stg[name].value
(lambda (alpha beta) (print alpha) (print beta))
>>> stg[name].value.environ['twirl'].value
(lambda (alpha beta) (print alpha) (print beta))
>>> stg['x'].value
10
>>> stg[name].value.environ['x'].value
Traceback (most recent call last):
...
KeyError: 'x'
"""
'''
if isinstance(se.car, Symbol):
if isinstance(se.cdr, Variable):
stg.put(str(se.car), se.cdr)
else:
f= lambda_func(se.cdr, stg)
f.environ.put(str(se.car), f)
else:
f= UserFunction(se.cdr, se.cdr.cdr, stg)
f.environ.put(str(se.car), f)
'''
'''
if isinstance(se.car, Symbol):
stg.put(str(se.car), se.cdr)
elif callable(se.car):
f= lambda_func(se.cdr, stg)
f.environ.put(str(se.car), f)
stg.put(str(se.car.car), f)
elif callable(se.car.car):
f= UserFunction(se.cdr, se.cdr.cdr, stg)
f.environ.put(str(se.car), f)
stg.put(str(se.car.car), f)
'''
if isinstance(se.car, SExpression):
f = UserFunction(se.car.cdr, se.cdr, stg.fork())
f.environ[str(se.car.car)] = Variable(f)
stg.put(str(se.car.car), f)
else:
f = lisp_eval(se.cdr.car, stg)
if isinstance(f, UserFunction):
f.environ[str(se.car)] = Variable(f)
stg.put(str(se.car), f)
else:
stg.put(str(se.car), f)
"""
