def full_evaluate(expression, environment):
"""
Fully evaluate an expression until its basic representation
"""
while True:
if is_thunk(expression):
if not expression.is_evaluated:
expression.is_evaluated = True
expression.expression = full_evaluate(expression.expression,
expression.environment)
return expression.expression
elif is_symbol(expression):
expression = environment[expression]
continue
elif (is_atom(expression) or is_nil(expression) or
is_procedure(expression) or is_macro(expression) or
callable(expression)):
return expression
elif not is_pair(expression):
raise ValueError("Cannot evaluate: %s" % expression)
elif car(expression) == 'delay':
if len(expression) != 2:
raise SyntaxError("Unexpected delay form: %s. Should be (delay <expression>)" %
expression)
return Thunk(cadr(expression), environment)
elif car(expression) == 'defined?':
if len(expression) != 2:
raise SyntaxError("Unexpected defined? form: %s. Should be (defined? <symbol>)" %
expression)
name = cadr(expression)
if not is_symbol(name):
raise SyntaxError("Argument of defined? form should be a symbol. Evaluating: %s" %
expression)
return environment.exists(name)
elif car(expression) == 'define':
if len(expression) != 3:
raise SyntaxError("Unexpected define form: %s. Should be (define <symbol> <expression>)" %
expression)
name = cadr(expression)
if not is_symbol(name):
raise SyntaxError("First argument of define form should be a symbol. Evaluating: %s" %
expression)
environment[name] = Thunk(caddr(expression), environment)
return name
elif car(expression) == 'quote':
if len(expression) != 2:
raise SyntaxError("Unexpected quote form: %s. Should be (quote <expression>)" %
expression)
return cadr(expression)
elif car(expression) == 'eval':
if len(expression) != 2:
raise SyntaxError("Unexpected eval form: %s. Should be (eval <expression>)" %
expression)
expression = full_evaluate(cadr(expression), environment)
continue
elif car(expression) == 'if':
if len(expression) != 4:
raise SyntaxError("Unexpected if form: %s. Should be (if <condition> <consequent> <alternative>)" %
expression)
condition = full_evaluate(cadr(expression), environment)
expression = caddr(expression) if condition else cadddr(expression)
continue
elif car(expression) == 'lambda':
if len(expression) < 3:
raise SyntaxError("Unexpected lambda form: %s. Should be (lambda (<param> ...) <expression> ...)" %
expression)
parameters = cadr(expression)
if is_pair(parameters):
current = parameters
while is_pair(current):
if not is_symbol(car(current)):
raise SyntaxError("Lambda parameters should be symbols. In %s" %
expression)
current = cdr(current)
if not is_nil(current) and not is_symbol(current):
raise SyntaxError("Lambda optional parameter should be a symbol or nil. In %s" %
expression)
elif not is_symbol(parameters) and not is_nil(parameters):
raise SyntaxError("Lambda parameters should be a symbol or a list of zero or more. In %s" %
expression)
return Procedure(parameters, # parameters
cddr(expression), # body (list of expressions)
environment)
elif car(expression) == 'macro':
if len(expression) < 3:
raise SyntaxError("Unexpected define macro: %s. Should be (macro (<resword> ...) (<pattern> <transformation> ...) ...)" %
expression)
res_words = cadr(expression)
rules = cddr(expression)
if not is_nil(res_words) and not is_pair(res_words):
raise SyntaxError("Macro reserved words should be a list of symbols or nil. In %s" %
expression)
if is_pair(res_words):
for word in res_words:
if not is_symbol(word):
raise SyntaxError("Macro reserved words should all be symbols. In %s" %
expression)
for rule in rules:
if len(rule) < 2:
raise SyntaxError("Macro rule should be in the form (<pattern> <expression> ...). In %s" %
expression)
return Macro( [(car(e), cdr(e)) for e in rules], # rules
[] if not res_words else set(iter(res_words)) ) # reserved words
else:
# evaluate head
operator = full_evaluate(car(expression), environment)
if is_macro(operator):
# evaluate recursively only the inner expressions (not the last)
current = operator.transform(expression)
while cdr(current) is not None:
full_evaluate(car(current), environment)
current = cdr(current)
expression = car(current)
continue
else:
# The unevaluated operands
unev_operands = cdr(expression)
if callable(operator):
# evaluate each operand recursively
operands = [full_evaluate(e, environment) for e in unev_operands] if unev_operands else []
# return the application of the built-in procedure
return operator(make_list(operands))
elif is_procedure(operator):
# create Thunks (promise to evaluate) for each operand
unev_op_list = list(iter(unev_operands)) if unev_operands else []
proc_environment = Environment(parent=operator.environment)
# if the lambda parameters is not in the format ( () [. <symbol>] )
# for taking zero or more arguments
if len(operator.parameters) != 1 or not is_nil(operator.parameters[0]):
for name in operator.parameters:
try:
# take next argument
proc_environment[name] = Thunk(unev_op_list.pop(0),
environment)
except IndexError:
raise ValueError("Insufficient parameters for procedure %s. It should be at least %d" %
(operator, len(operator.parameters)))
if not is_nil(operator.optional):
# the optional argument is something, that when
# evaluated, yields the list of rest of the operands
# evaluated
proc_environment[operator.optional] = Thunk(cons(lambda x: x,
make_list(unev_op_list)),
environment)
elif unev_op_list:
raise ValueError("Too much parameters for procedure %s. It should be %d." %
(operator, len(operator.parameters)))
# evaluate recursively only the inner procedure expressions
# (not the last)
current = operator.body
while cdr(current) is not None:
full_evaluate(car(current), proc_environment)
current = cdr(current)
environment = proc_environment
expression = car(current)
# continue not-recursively to evaluate the procedure's body
# in the extended environment
continue
else:
raise ValueError("Not an operator: %s, in expression: %s" %
(operator, expression))
def make_global_environment():
env = NumericEnvironment()
# utf-8 stdin and out
stdin = codecs.getreader('utf-8')(sys.stdin)
stdout = codecs.getreader('utf-8')(sys.stdout)
env.update({
# built-in symbols
'nil':
None,
'#t':
True,
'#f':
False,
# symbolic tests
'procedure?':
BuiltinProcedure(lambda args: is_procedure(car(args)), 'procedure?', 1,
1),
'macro?':
BuiltinProcedure(lambda args: is_macro(car(args)), 'macro?', 1, 1),
'thunk?':
BuiltinProcedure(lambda args: is_thunk(car(args)), 'thunk?', 1, 1),
'symbol?':
BuiltinProcedure(lambda args: is_symbol(car(args)), 'symbol?', 1, 1),
'atom?':
BuiltinProcedure(lambda args: is_atom(car(args)), 'atom?', 1, 1),
'pair?':
BuiltinProcedure(lambda args: is_pair(car(args)), 'pair?', 1, 1),
'nil?':
BuiltinProcedure(lambda args: is_nil(car(args)), 'nil?', 1, 1),
'eq?':
BuiltinProcedure(lambda args: car(args) is cadr(args), 'eq?', 2, 2),
'=':
BuiltinProcedure(lambda args: car(args) == cadr(args), '=', 2, 2),
# symbolic manipulation
'explode':
BuiltinProcedure(lambda args: make_list(list(car(args))), 'explode', 1,
1),
'implode':
BuiltinProcedure(lambda args: ''.join(iter(args)), 'implode', 1),
# basic data manipulation
'car':
BuiltinProcedure(lambda args: caar(args), 'car', 1, 1),
"cdr":
BuiltinProcedure(lambda args: cdar(args), "cdr", 1, 1),
"cons":
BuiltinProcedure(lambda args: cons(car(args), cadr(args)), "cons", 2,
2),
# I/O operations
'write':
BuiltinProcedure(
lambda args: stdout.write(
unicode(car(args)).encode('utf-8').decode('string_escape')),
'write', 1, 1),
'read':
BuiltinProcedure(lambda args: stdin.read(1), 'read', 0, 0),
'file-open':
BuiltinProcedure(
lambda args: codecs.open(car(args), cadr(args), 'utf-8'),
'file-open', 2, 2),
'file-close':
BuiltinProcedure(lambda args: car(args).close(), 'file-close', 1, 1),
'file-write':
BuiltinProcedure(
lambda args: car(args).write(
unicode(cadr(args)).encode('utf-8').decode('string_escape').
decode('utf-8')), 'file-write', 2, 2),
'file-read':
BuiltinProcedure(lambda args: car(args).read(1), 'file-read', 1, 1),
# dependency inclusion
'include':
IncludeMacro(),
# arithmetic operations
'+':
BuiltinProcedure(lambda args: reduce(operator.add, args), '+', 2),
'-':
BuiltinProcedure(lambda args: reduce(operator.sub, args), '-', 2),
'*':
BuiltinProcedure(lambda args: reduce(operator.mul, args), '*', 2),
'/':
BuiltinProcedure(lambda args: reduce(operator.div, args), '/', 2),
'mod':
BuiltinProcedure(lambda args: reduce(operator.mod, args), 'mod', 2),
'<':
BuiltinProcedure(lambda args: car(args) < cadr(args), '<', 2),
'>':
BuiltinProcedure(lambda args: car(args) > cadr(args), '>', 2),
'<=':
BuiltinProcedure(lambda args: car(args) <= cadr(args), '<=', 2),
'>=':
BuiltinProcedure(lambda args: car(args) >= cadr(args), '>=', 2),
})
return env
def make_global_environment():
env = NumericEnvironment()
# utf-8 stdin and out
stdin = codecs.getreader("utf-8")(sys.stdin)
stdout = codecs.getreader("utf-8")(sys.stdout)
env.update(
{
# built-in symbols
"nil": None,
"#t": True,
"#f": False,
# symbolic tests
"procedure?": BuiltinProcedure(lambda args: is_procedure(car(args)), "procedure?", 1, 1),
"macro?": BuiltinProcedure(lambda args: is_macro(car(args)), "macro?", 1, 1),
"thunk?": BuiltinProcedure(lambda args: is_thunk(car(args)), "thunk?", 1, 1),
"symbol?": BuiltinProcedure(lambda args: is_symbol(car(args)), "symbol?", 1, 1),
"atom?": BuiltinProcedure(lambda args: is_atom(car(args)), "atom?", 1, 1),
"pair?": BuiltinProcedure(lambda args: is_pair(car(args)), "pair?", 1, 1),
"nil?": BuiltinProcedure(lambda args: is_nil(car(args)), "nil?", 1, 1),
"eq?": BuiltinProcedure(lambda args: car(args) is cadr(args), "eq?", 2, 2),
"=": BuiltinProcedure(lambda args: car(args) == cadr(args), "=", 2, 2),
# symbolic manipulation
"explode": BuiltinProcedure(lambda args: make_list(list(car(args))), "explode", 1, 1),
"implode": BuiltinProcedure(lambda args: "".join(iter(args)), "implode", 1),
# basic data manipulation
"car": BuiltinProcedure(lambda args: caar(args), "car", 1, 1),
"cdr": BuiltinProcedure(lambda args: cdar(args), "cdr", 1, 1),
"cons": BuiltinProcedure(lambda args: cons(car(args), cadr(args)), "cons", 2, 2),
# I/O operations
"write": BuiltinProcedure(
lambda args: stdout.write(unicode(car(args)).encode("utf-8").decode("string_escape")), "write", 1, 1
),
"read": BuiltinProcedure(lambda args: stdin.read(1), "read", 0, 0),
"file-open": BuiltinProcedure(lambda args: codecs.open(car(args), cadr(args), "utf-8"), "file-open", 2, 2),
"file-close": BuiltinProcedure(lambda args: car(args).close(), "file-close", 1, 1),
"file-write": BuiltinProcedure(
lambda args: car(args).write(
unicode(cadr(args)).encode("utf-8").decode("string_escape").decode("utf-8")
),
"file-write",
2,
2,
),
"file-read": BuiltinProcedure(lambda args: car(args).read(1), "file-read", 1, 1),
# dependency inclusion
"include": IncludeMacro(),
# arithmetic operations
"+": BuiltinProcedure(lambda args: reduce(operator.add, args), "+", 2),
"-": BuiltinProcedure(lambda args: reduce(operator.sub, args), "-", 2),
"*": BuiltinProcedure(lambda args: reduce(operator.mul, args), "*", 2),
"/": BuiltinProcedure(lambda args: reduce(operator.div, args), "/", 2),
"mod": BuiltinProcedure(lambda args: reduce(operator.mod, args), "mod", 2),
"<": BuiltinProcedure(lambda args: car(args) < cadr(args), "<", 2),
">": BuiltinProcedure(lambda args: car(args) > cadr(args), ">", 2),
"<=": BuiltinProcedure(lambda args: car(args) <= cadr(args), "<=", 2),
">=": BuiltinProcedure(lambda args: car(args) >= cadr(args), ">=", 2),
}
)
return env
def full_evaluate(expression, environment):
"""
Fully evaluate an expression until its basic representation
"""
while True:
if is_thunk(expression):
if not expression.is_evaluated:
expression.is_evaluated = True
expression.expression = full_evaluate(expression.expression,
expression.environment)
return expression.expression
elif is_symbol(expression):
expression = environment[expression]
continue
elif (is_atom(expression) or is_nil(expression)
or is_procedure(expression) or is_macro(expression)
or callable(expression)):
return expression
elif not is_pair(expression):
raise ValueError("Cannot evaluate: %s" % expression)
elif car(expression) == 'delay':
if len(expression) != 2:
raise SyntaxError(
"Unexpected delay form: %s. Should be (delay <expression>)"
% expression)
return Thunk(cadr(expression), environment)
elif car(expression) == 'defined?':
if len(expression) != 2:
raise SyntaxError(
"Unexpected defined? form: %s. Should be (defined? <symbol>)"
% expression)
name = cadr(expression)
if not is_symbol(name):
raise SyntaxError(
"Argument of defined? form should be a symbol. Evaluating: %s"
% expression)
return environment.exists(name)
elif car(expression) == 'define':
if len(expression) != 3:
raise SyntaxError(
"Unexpected define form: %s. Should be (define <symbol> <expression>)"
% expression)
name = cadr(expression)
if not is_symbol(name):
raise SyntaxError(
"First argument of define form should be a symbol. Evaluating: %s"
% expression)
environment[name] = Thunk(caddr(expression), environment)
return name
elif car(expression) == 'quote':
if len(expression) != 2:
raise SyntaxError(
"Unexpected quote form: %s. Should be (quote <expression>)"
% expression)
return cadr(expression)
elif car(expression) == 'eval':
if len(expression) != 2:
raise SyntaxError(
"Unexpected eval form: %s. Should be (eval <expression>)" %
expression)
expression = full_evaluate(cadr(expression), environment)
continue
elif car(expression) == 'if':
if len(expression) != 4:
raise SyntaxError(
"Unexpected if form: %s. Should be (if <condition> <consequent> <alternative>)"
% expression)
condition = full_evaluate(cadr(expression), environment)
expression = caddr(expression) if condition else cadddr(expression)
continue
elif car(expression) == 'lambda':
if len(expression) < 3:
raise SyntaxError(
"Unexpected lambda form: %s. Should be (lambda (<param> ...) <expression> ...)"
% expression)
parameters = cadr(expression)
if is_pair(parameters):
current = parameters
while is_pair(current):
if not is_symbol(car(current)):
raise SyntaxError(
"Lambda parameters should be symbols. In %s" %
expression)
current = cdr(current)
if not is_nil(current) and not is_symbol(current):
raise SyntaxError(
"Lambda optional parameter should be a symbol or nil. In %s"
% expression)
elif not is_symbol(parameters) and not is_nil(parameters):
raise SyntaxError(
"Lambda parameters should be a symbol or a list of zero or more. In %s"
% expression)
return Procedure(
parameters, # parameters
cddr(expression), # body (list of expressions)
environment)
elif car(expression) == 'macro':
if len(expression) < 3:
raise SyntaxError(
"Unexpected define macro: %s. Should be (macro (<resword> ...) (<pattern> <transformation> ...) ...)"
% expression)
res_words = cadr(expression)
rules = cddr(expression)
if not is_nil(res_words) and not is_pair(res_words):
raise SyntaxError(
"Macro reserved words should be a list of symbols or nil. In %s"
% expression)
if is_pair(res_words):
for word in res_words:
if not is_symbol(word):
raise SyntaxError(
"Macro reserved words should all be symbols. In %s"
% expression)
for rule in rules:
if len(rule) < 2:
raise SyntaxError(
"Macro rule should be in the form (<pattern> <expression> ...). In %s"
% expression)
return Macro(
[(car(e), cdr(e)) for e in rules], # rules
[]
if not res_words else set(iter(res_words))) # reserved words
else:
# evaluate head
operator = full_evaluate(car(expression), environment)
if is_macro(operator):
# evaluate recursively only the inner expressions (not the last)
current = operator.transform(expression)
while cdr(current) is not None:
full_evaluate(car(current), environment)
current = cdr(current)
expression = car(current)
continue
else:
# The unevaluated operands
unev_operands = cdr(expression)
if callable(operator):
# evaluate each operand recursively
operands = [
full_evaluate(e, environment) for e in unev_operands
] if unev_operands else []
# return the application of the built-in procedure
return operator(make_list(operands))
elif is_procedure(operator):
# create Thunks (promise to evaluate) for each operand
unev_op_list = list(
iter(unev_operands)) if unev_operands else []
proc_environment = Environment(parent=operator.environment)
# if the lambda parameters is not in the format ( () [. <symbol>] )
# for taking zero or more arguments
if len(operator.parameters) != 1 or not is_nil(
operator.parameters[0]):
for name in operator.parameters:
try:
# take next argument
proc_environment[name] = Thunk(
unev_op_list.pop(0), environment)
except IndexError:
raise ValueError(
"Insufficient parameters for procedure %s. It should be at least %d"
% (operator, len(operator.parameters)))
if not is_nil(operator.optional):
# the optional argument is something, that when
# evaluated, yields the list of rest of the operands
# evaluated
proc_environment[operator.optional] = Thunk(
cons(lambda x: x, make_list(unev_op_list)),
environment)
elif unev_op_list:
raise ValueError(
"Too much parameters for procedure %s. It should be %d."
% (operator, len(operator.parameters)))
# evaluate recursively only the inner procedure expressions
# (not the last)
current = operator.body
while cdr(current) is not None:
full_evaluate(car(current), proc_environment)
current = cdr(current)
environment = proc_environment
expression = car(current)
# continue not-recursively to evaluate the procedure's body
# in the extended environment
continue
else:
raise ValueError("Not an operator: %s, in expression: %s" %
(operator, expression))