def eval_math_operators(ast, env):
exprs = {
"+" : lambda a, b: evaluate(a, env) + evaluate(b, env),
"-" : lambda a, b: evaluate(a, env) - evaluate(b, env),
"*" : lambda a, b: evaluate(a, env) * evaluate(b, env),
"/" : lambda a, b: evaluate(a, env) / evaluate(b, env),
"mod" : lambda a, b: evaluate(a, env) % evaluate(b, env),
">" : lambda a, b: evaluate(a, env) > evaluate(b, env)
}
arg1 = evaluate(ast[1], env)
arg2 = evaluate(ast[2], env)
if not(is_integer(arg1)) or not(is_integer(arg2)):
raise LispError("Arithmetic operations only work on integers")
return exprs.get(ast[0], err_syntax)(arg1, arg2)
def assert_int(x, env):
x = evaluate(x, env)
if is_integer(x):
return x
else:
raise LispError("Expected integer but got: %s" % x)
def evaluate(ast, env):
"""Evaluate an Abstract Syntax Tree in the specified environment."""
if is_boolean(ast) or is_integer(ast):
return ast
elif is_symbol(ast):
return env.lookup(ast)
if not is_atom(ast[0]):
ast[0] = evaluate(ast[0], env)
elif is_symbol(ast[0]):
if ast[0] in keywords:
return keywords[ast[0]](ast, env)
elif ast[0] in math_operators:
return eval_math(ast, env)
else:
ast[0] = env.lookup(ast[0])
if is_closure(ast[0]):
args = [evaluate(x, env) for x in ast[1:]]
num_args = len(args)
num_params = len(ast[0].params)
if num_args != num_params:
raise LispError('wrong number of arguments, expected %d got %d'
% (num_params, num_args))
bindings = dict(zip(ast[0].params, args))
return evaluate(ast[0].body, ast[0].env.extend(bindings))
raise LispError('not a function: %s' % unparse(ast[0]))
def eval_math_operation(symbol, args, env):
eval1 = evaluate(args[0],env)
eval2 = evaluate(args[1],env)
if not (is_integer(eval1) and is_integer(eval2)):
raise LispError('math operands must be an integer values')
if symbol == "+":
return eval1 + eval2
elif symbol == "-":
return eval1 - eval2
elif symbol == "/":
return eval1 / eval2
elif symbol == "*":
return eval1 * eval2
elif symbol == "mod":
return eval1 % eval2
else:
return eval1
def eval_math(ast, env):
"""Evaluate an mathematical operator and its
arguments in the specified environment.
Mathematical operations are carried out by the corresponding
mathematical operators built into python.
"""
a1 = evaluate(ast[1], env)
a2 = evaluate(ast[2], env)
if is_integer(a1) and is_integer(a2):
operators = {
'+': add,
'-': sub,
'/': floordiv,
'*': mul,
'mod': opmod,
'>': gt,
'<': lt,
'=': opeq}
return operators[ast[0]](a1, a2)
else:
raise LispError("Math operators only work on integers!")
def evaluate(ast, env):
"""Evaluate an Abstract Syntax Tree in the specified environment."""
if is_integer(ast):
return ast
elif ast[0] == "quote":
return ast[1]
elif ast[0] == "atom":
return atom(ast[1], env)
elif ast[0] == "eq":
first = evaluate(ast[1], env)
second = evaluate(ast[2], env)
return first == second
elif ast[0] == "+":
return do_math(ast, op.add, env)
elif ast[0] == "-":
return do_math(ast, op.sub, env)
elif ast[0] == "/":
return do_math(ast, op.div, env)
elif ast[0] == "*":
return do_math(ast, op.mul, env)
elif ast[0] == "mod":
return do_math(ast, op.mod, env)
elif ast[0] == ">":
return do_math(ast, op.gt, env)
elif ast[0] == "if":
return do_if(ast, env)
elif ast[0] == "define":
define(ast, env)
elif ast[0] == "lambda":
return closure(ast, env)
elif ast[0] == "cons":
return cons(ast, env)
elif ast[0] == "car":
return car(ast, env)
elif ast[0] == "cdr":
return cdr(ast, env)
elif is_closure(ast[0]):
return evaluate_closure(ast, env)
elif is_list(ast):
return evaluate_function(ast, env)
else:
return env.lookup(ast)
def evaluate(ast, env):
"""Evaluate an Abstract Syntax Tree in the specified environment."""
if is_symbol(ast):
return env.lookup(ast)
elif is_boolean(ast) or is_integer(ast):
return ast
elif is_closure(ast):
return evalClosure(ast, [], env)
elif is_list(ast) and len(ast) > 0:
first = ast[0]
# handle string commands
if isinstance(first, basestring):
if first in commands:
return evalCommand(first, ast[1:], env)
# When a non-keyword symbol is the first element of the AST list, it is resolved to its value in
# the environment (which should be a function closure). An AST with the variables
# replaced with its value should then be evaluated instead.
else:
func = env.lookup(first)
if not is_closure(func):
raise LispError("Symbol %s must evaluate to a function" % first)
ast[0] = func
return evaluate(ast, env)
# handle closure objects
elif is_closure(first):
return evalClosure(first, ast[1:], env)
else: # otherwise - evaluate the first expression on the list
firstEval = evaluate(first, env);
if is_closure(firstEval): # if closure - treat the rest of the list as arguments
return evalClosure(first, ast[1:], env)
else : # not a closure, just evaluate the rest of the list and return the last expression
if len(ast) > 1:
return evaluate(ast[1:], env)
else:
return firstEval
raise LispError("Invalid AST: %s" % ast)
def evaluate(ast, env):
"""Evaluate an Abstract Syntax Tree in the specified environment."""
if is_boolean(ast):
return ast
elif is_integer(ast):
return ast
elif ast[0] in ['+', '-', '*', '/']:
return eval_math(ast, env)
elif is_list(ast):
if ast[0] == "atom":
return is_atom(evaluate(ast[1], env))
#return is_atom(ast[1])
elif ast[0] == "quote":
return ast[1]
elif ast[0] == "eq":
assert_exp_length(ast, 3)
v1 = evaluate(ast[1], env)
v2 = evaluate(ast[2], env)
if not is_atom(v1) or not is_atom(v2):
return False
else:
return (v1 == v2)
def evaluate(ast, env):
"""Evaluate an Abstract Syntax Tree in the specified environment.
"""
if is_boolean(ast) or is_integer(ast): # evaluate booleans and integers
return ast
elif is_symbol(ast): # evaluate symbols
return env.lookup(ast)
elif is_list(ast): # evaluate lists
if is_closure(ast[0]): # evaluate closure
return eval_closure(ast, env)
elif ast[0] == 'quote': # evaluate quotes
return ast[1]
elif ast[0] == 'atom': # evaluate atoms
return is_atom(evaluate(ast[1], env))
elif ast[0] == 'eq': # evaluate equality
return eval_eq(ast, env)
# evaluate basic math operators:
elif ast[0] in ['+', '-', '/', '*', 'mod', '>', '<', '=']:
return eval_math(ast, env)
elif ast[0] == 'if': # evaluate if expression
return eval_if(ast, env)
elif ast[0] == 'define': # evaluate define statement
eval_define(ast, env)
elif ast[0] == 'lambda': # evaluate lambda statement
return eval_lambda(ast, env)
elif ast[0] == 'cons': # evaluate cons statement
return eval_cons(ast, env)
elif ast[0] == 'head': # evaluate head statement
return eval_head(ast, env)
elif ast[0] == 'tail': # evaluate tail statement
return eval_tail(ast, env)
elif ast[0] == 'empty': # evaluate empty statement
return eval_empty(ast, env)
elif is_symbol(ast[0]) or is_list(ast[0]): # evaluate closure from env
return eval_closure_env(ast, env)
else:
raise LispError('Argument is not a function!')
def evaluate(ast, env):
"""Evaluate an Abstract Syntax Tree in the specified environment."""
# evaluating atoms
if is_symbol(ast):
return env.lookup(ast)
if is_boolean(ast):
return ast
if is_integer(ast):
return ast
if is_list(ast):
# lists
if ast[0] == "cons":
if len(ast) != 3:
raise LispError("expected 2 arguments")
else:
value = evaluate(ast[1], env)
list = evaluate(ast[2], env)
new_list = [value]
for i in list:
new_list.append(i)
return new_list
if ast[0] == "head":
list = evaluate(ast[1], env)
if list == []:
raise LispError
else: return list[0]
if ast[0] == "tail":
list = evaluate(ast[1], env)
if list == []:
raise LispError
else: return list[1:]
if ast[0] == "empty":
list = evaluate(ast[1], env)
if list == []:
return True
else: return False
if ast[0] == "quote":
return ast[1]
# functions
if is_closure(ast[0]):
closure = ast[0]
arguments = ast[1:]
params = closure.params
number_of_arguments = len(arguments)
number_of_params = len(params)
if number_of_arguments != number_of_params:
raise LispError("wrong number of arguments, expected %(param)d got %(arg)d" %
{"arg": number_of_arguments, "param": number_of_params})
variables = {}
for i in range(number_of_arguments):
arg = evaluate(arguments[i], env)
param = params[i]
variables.update({param: arg})
environment = closure.env.extend(variables)
return evaluate(closure.body, environment)
if ast[0] == "lambda":
if not is_list(ast[1]):
raise LispError
if len(ast) == 3:
return Closure(env, ast[1], ast[2])
else:
raise LispError("number of arguments")
# defining variables
if ast[0] == "define":
if is_symbol(ast[1]):
if len(ast) == 3:
return env.set(ast[1], evaluate(ast[2], env))
else:
raise LispError("Wrong number of arguments")
else:
raise LispError("non-symbol")
#typechecks
if ast[0] == "atom":
return is_atom(evaluate(ast[1], env))
if ast[0] == "eq":
return evaluate(ast[1], env) == evaluate(ast[2], env) and \
is_atom(evaluate(ast[1], env)) and is_atom(evaluate(ast[2], env))
#arithmetic:
# elif is_arith_op(ast[0]):
# try:
# return arith_ops[ast[0]](evaluate(ast[1], env), evaluate(ast[2], env))
# make dicitonary of these operators
if ast[0] == "+":
if is_integer(evaluate(ast[1], env)) and is_integer(evaluate(ast[2], env)):
return evaluate(ast[1], env) + evaluate(ast[2], env)
else:
raise LispError
if ast[0] == "-":
if is_integer(evaluate(ast[1], env)) and is_integer(evaluate(ast[2], env)):
return evaluate(ast[1], env) - evaluate(ast[2], env)
else:
raise LispError
if ast[0] == "*":
if is_integer(evaluate(ast[1], env)) and is_integer(evaluate(ast[2], env)):
return evaluate(ast[1], env) * evaluate(ast[2], env)
else:
raise LispError
if ast[0] == "/":
if is_integer(evaluate(ast[1], env)) and is_integer(evaluate(ast[2], env)):
return evaluate(ast[1], env) / evaluate(ast[2], env)
else:
raise LispError
if ast[0] == "mod":
if is_integer(evaluate(ast[1], env)) and is_integer(evaluate(ast[2], env)):
return evaluate(ast[1], env) % evaluate(ast[2], env)
else:
raise LispError
# boolean operators
if ast[0] == ">":
return evaluate(ast[1], env) > evaluate(ast[2], env)
if ast[0] == "<":
return evaluate(ast[1], env) < evaluate(ast[2], env)
# control-flow
if ast[0] == 'if':
pred = ast[1]
then = ast[2]
elsee = ast[3]
if evaluate(pred, env):
return evaluate(then, env)
else:
return evaluate(elsee, env)
if is_symbol(ast[0]) or is_list(ast[0]):
closure = evaluate(ast[0], env)
return evaluate([closure] + ast[1:], env)
else:
raise LispError("not a function")
def evaluate(ast, env):
"""Evaluate an Abstract Syntax Tree in the specified environment."""
if ast == "#t":
return True
if ast == "#f":
return False
if is_symbol(ast):
symbol_value = env.lookup(ast)
# if is_closure(symbol_value):
# return evaluate(symbol_value, env)
return symbol_value
if is_integer(ast):
return ast
first_element = ast[0]
if first_element == "quote":
if len(ast) == 2:
return ast[1]
else:
return []
if first_element == "atom":
return is_atom(evaluate(ast[1], env))
if first_element == "if":
if evaluate(ast[1], env):
return evaluate(ast[2], env)
else:
return evaluate(ast[3], env)
if first_element == "define":
if len(ast) != 3:
raise LispError("Wrong number of arguments")
symbol_name = ast[1]
if not is_symbol(symbol_name):
raise LispError("non-symbol")
value = evaluate(ast[2], env)
env.set(symbol_name, value)
return value
if first_element == "eq":
evaluated_items = [evaluate(item, env) for item in ast[1:]]
for i in range(len(evaluated_items) - 1):
return is_atom(evaluated_items[i]) and evaluated_items[i] == evaluated_items[i + 1]
else:
return True
if first_element in ["+", "-", "*", "/", "mod", "<", ">"] and not (is_integer(evaluate(ast[1], env)) and is_integer(
evaluate(ast[2], env))):
error_message = "Math functions only take integer args but you tried to do (%s, %s, %s)" % (
first_element, (evaluate(ast[1], env)), (evaluate(ast[2], env)))
raise LispError(error_message)
if first_element == "+":
return evaluate(ast[1], env) + evaluate(ast[2], env)
if first_element == "-":
return evaluate(ast[1], env) - evaluate(ast[2], env)
if first_element == "*":
return evaluate(ast[1], env) * evaluate(ast[2], env)
if first_element == "/":
return evaluate(ast[1], env) / evaluate(ast[2], env)
if first_element == "mod":
return evaluate(ast[1], env) % evaluate(ast[2], env)
if first_element == ">":
return evaluate(ast[1], env) > evaluate(ast[2], env)
if first_element == "<":
return evaluate(ast[1], env) < evaluate(ast[2], env)
# List functions
if first_element == "cons":
if len(ast) != 3:
raise LispError("cons requires 2 arguments")
element = evaluate(ast[1], env)
list = evaluate(ast[2], env)
if not is_list(list):
raise LispError("cons requires second arg to be list but got %s" % unparse(ast[2]))
list.insert(0, element)
return list
if first_element == "head":
if len(ast) != 2:
raise LispError("head requires 1 argument")
list_expression = evaluate(ast[1], env)
if not is_list(list_expression) or len(list_expression) < 1:
raise LispError("head requires a list of at least length 1")
return list_expression[0]
if first_element == "tail":
if len(ast) != 2:
raise LispError("tail requires 1 argument")
list_expression = evaluate(ast[1], env)
if not is_list(list_expression) or len(list_expression) < 1:
raise LispError("tail requires a list argument")
return list_expression[1:]
if first_element == "empty":
if len(ast) != 2:
raise LispError("empty requires 1 argument")
list_expression = evaluate(ast[1], env)
if not is_list(list_expression):
raise LispError("empty requires a list argument")
return len(list_expression) == 0
# Function functions
if first_element == "lambda":
if len(ast) != 3:
raise LispError("number of arguments")
params = ast[1]
if not is_list(params):
raise LispError("params must be a list")
body = ast[2]
return Closure(env, params, body)
if first_element == "quit":
raise QuitError("Bye!")
if first_element == "print":
print "".join((str(evaluate(i, env)) for i in ast[1:]))
return []
if first_element == "pp":
print " ".join((str(evaluate(i, env)) for i in ast[1:]))
return []
if first_element == "do":
for i in ast[1:-1]:
evaluate(i, env)
return evaluate(ast[-1], env)
if is_list(ast):
if len(ast) == 0:
return []
if is_symbol(first_element) and env.has_symbol(first_element):
closure = env.lookup(first_element)
elif is_closure(first_element):
closure = first_element
else:
closure = evaluate(first_element, env)
if not is_closure(closure):
raise LispError("not a function")
argument_bindings = {}
if len(ast) > 1:
param_values = ast[1:]
closure_params = closure.params
if len(closure_params) != len(param_values):
raise LispError("wrong number of arguments, expected %i got %i" % (len(closure_params), len(param_values)))
for i in range(len(closure_params)):
param_name = closure_params[i]
argument_bindings[param_name] = evaluate(param_values[i], env)
result = evaluate(closure.body, closure.env.extend(argument_bindings))
if is_closure(result):
return evaluate(result.body, result.env)
return result
def _evaluate_math(ast, env):
func = MATH_EXP[ast[0]]
a1, a2 = evaluate(ast[1], env), evaluate(ast[2], env)
if not is_integer(a1) or not is_integer(a2):
raise LispError('You can only do math on numbers')
return func(a1, a2)
def evaluate(ast, env):
"""Evaluate an Abstract Syntax Tree in the specified environment."""
# evaluating booleans, integers, symbols and quotes
if is_boolean(ast):
return ast
elif is_integer(ast):
return ast
elif is_symbol(ast):
return env.lookup(ast)
elif ast[0] == "quote":
return ast[1]
# everything else is of list form
elif is_list(ast):
# evaluating atom and eq functions
if ast[0] == "atom":
return is_atom(evaluate(ast[1], env))
elif ast[0] == "eq":
aste = [evaluate(s, env) for s in ast[1:]]
return is_atom(aste[0]) and aste[0] == aste[1]
# evaluating basic math operators
elif ast[0] == "+":
if is_integer(evaluate(ast[1], env)) and is_integer(evaluate(ast[2], env)):
return evaluate(ast[1], env) + evaluate(ast[2], env)
else:
raise LispError('Arguments must be integers')
elif ast[0] == "-":
if is_integer(evaluate(ast[1], env)) and is_integer(evaluate(ast[2], env)):
return evaluate(ast[1], env) - evaluate(ast[2], env)
else:
raise LispError('Arguments must be integers')
elif ast[0] == "*":
if is_integer(evaluate(ast[1], env)) and is_integer(evaluate(ast[2], env)):
return evaluate(ast[1], env) * evaluate(ast[2], env)
else:
raise LispError('Arguments must be integers')
elif ast[0] == "mod":
if is_integer(evaluate(ast[1], env)) and is_integer(evaluate(ast[2], env)):
return evaluate(ast[1], env) % evaluate(ast[2], env)
else:
raise LispError('Arguments must be integers')
elif ast[0] == "/":
if is_integer(evaluate(ast[1], env)) and is_integer(evaluate(ast[2], env)):
return evaluate(ast[1], env) / evaluate(ast[2], env)
else:
raise LispError('Arguments must be integers')
elif ast[0] == ">":
return evaluate(ast[1], env) > evaluate(ast[2], env)
elif ast[0] == "<":
return evaluate(ast[1], env) < evaluate(ast[2], env)
# Evaluating complex expressions
# basic if statement
elif ast[0] == 'if':
if (evaluate(ast[1], env)) is True:
return evaluate(ast[2], env)
else:
return evaluate(ast[3], env)
# definitions of variables
elif ast[0] == "define":
if is_symbol(ast[1]):
if len(ast) == 3:
return env.set(ast[1], evaluate(ast[2], env))
else:
raise LispError("Wrong number of arguments")
else:
raise LispError("non-symbol")
# evaluating a list in which the first element is a closure
elif is_closure(ast[0]):
closure = ast[0]
arguments = ast[1:]
parameters = closure.params
if len(arguments) != len(parameters):
raise LispError('wrong number of arguments, expected 2 got 3')
bindings = {}
for x in range(len(ast[1:])):
arg1 = evaluate(arguments[x], env)
param1 = parameters[x]
bindings.update({param1: arg1})
return evaluate(closure.body, closure.env.extend(bindings))
elif ast[0] == 'lambda':
if not is_list(ast[1]):
raise LispError('not a list')
if len(ast) == 3:
return Closure(env, ast[1], ast[2])
else:
raise LispError('number of arguments')
# new forms such as cons, head, tail and empty
elif ast[0] == "cons":
if len(ast) != 3:
raise LispError("expected 2 arguments")
else:
list = [evaluate(x, env) for x in ast[1:]]
return [list[0]] + list[1]
elif ast[0] == "head":
list = [evaluate(x, env) for x in ast[1:]]
if list[0] == []:
raise LispError('empty list')
return list[0][0]
elif ast[0] == "tail":
list = evaluate(ast[1], env)
if list == []:
raise LispError('empty list')
else:
return list[1:]
elif ast[0] == "empty":
list = evaluate(ast[1], env)
return (list == [])
elif is_symbol(ast[0]) or is_list(ast[0]):
closure = evaluate(ast[0], env)
return evaluate([closure] + ast[1:], env)
else:
raise LispError("not a function")
def eval_math(ast, env):
args = [evaluate(x, env) for x in ast[1:]]
if not (reduce(operator.and_, [is_integer(x) for x in args])):
raise LispError('Arguments must be integers.')
return reduce(math_operators[ast[0]], args)
def evaluate(ast, env):
"""Evaluate an Abstract Syntax Tree in the specified environment."""
if is_boolean(ast) or is_integer(ast):
return ast
elif is_symbol(ast):
return env.lookup(ast)
elif is_list(ast):
f = ast[0]
params = ast[1:]
if is_list(f):
c = evaluate(f, env)
return evaluate([c] + params, env)
elif f == 'quote':
return params[0]
elif f == 'atom':
return is_atom(evaluate(params[0], env))
elif f == 'if':
test = evaluate(params[0], env)
if not is_boolean(test):
raise LispError("First argument to if must be boolean")
if test:
return evaluate(params[1], env)
else:
return evaluate(params[2], env)
elif f == 'define':
if len(params) != 2:
raise LispError("Wrong number of arguments")
elif not is_symbol(params[0]):
raise LispError("First argument to define is a non-symbol")
env.set(params[0], evaluate(params[1], env))
elif f == 'lambda':
if len(params) != 2:
raise LispError("Wrong number of arguments")
return Closure(env, params[0], params[1])
elif is_closure(f):
evaled_params = {}
for i, symbol in enumerate(f.params):
evaled_params[symbol] = evaluate(params[i], env)
return evaluate(f.body, f.env.extend(evaled_params))
elif is_symbol(f):
evaled = evaluate(f, env)
if callable(evaled): # python function
evaled_params = []
for p in params:
evaled_params.append(evaluate(p, env))
return evaled(*evaled_params)
elif is_closure(evaled):
expected_arg_length = len(evaled.params)
actual_arg_length = len(params)
if expected_arg_length != actual_arg_length:
raise LispError("wrong number of arguments, expected " + str(expected_arg_length) + " got " + str(actual_arg_length))
return evaluate([evaled] + params, env)
else:
raise LispError()
else:
raise LispError(str(ast) + "is not a function")
else:
raise LispError("xxx")
def evaluate(ast, env):
"""Evaluate an Abstract Syntax Tree in the specified environment."""
# Simple types
if is_symbol(ast):
splitast = ast.split(' ')
if splitast[0] == 'define':
return Environment.extend(env, dict(zip(splitast[1:2], splitast[2::])))
else:
return Environment.lookup(env, ast)
if is_boolean(ast) or is_integer(ast):
return ast
if is_list(ast):
# Basic arithmetic
if ast[0] == '+':
if is_integer(evaluate(ast[1], env)) and is_integer(evaluate(ast[2], env)):
return evaluate(ast[1], env) + evaluate(ast[2], env)
if ast[0] == '-':
if is_integer(evaluate(ast[1], env)) and is_integer(evaluate(ast[2], env)):
return evaluate(ast[1], env) - evaluate(ast[2], env)
if ast[0] == '/':
if is_integer(evaluate(ast[1], env)) and is_integer(evaluate(ast[2], env)):
return evaluate(ast[1], env) / evaluate(ast[2], env)
if ast[0] == '*':
if is_integer(evaluate(ast[1], env)) and is_integer(evaluate(ast[2], env)):
return evaluate(ast[1], env) * evaluate(ast[2], env)
if ast[0] == 'mod':
if is_integer(evaluate(ast[1], env)) and is_integer(evaluate(ast[2], env)):
return evaluate(ast[1], env) % evaluate(ast[2], env)
if ast[0] == '>':
if is_integer(evaluate(ast[1], env)) and is_integer(evaluate(ast[2], env)):
return evaluate(ast[1], env) > evaluate(ast[2], env)
if ast[0] == '<':
if is_integer(evaluate(ast[1], env)) and is_integer(evaluate(ast[2], env)):
return evaluate(ast[1], env) < evaluate(ast[2], env)
# Atoms, quotes and equal
if ast[0] == 'atom':
return is_atom(evaluate(ast[1], env))
if ast[0] == 'quote':
return ast[1]
if ast[0] == 'eq':
return ( is_atom(evaluate(ast[1], env)) and is_atom(evaluate(ast[2], env))
and evaluate(ast[1], env) == evaluate(ast[2], env) )
# If statement
if ast[0] == 'if':
if evaluate(ast[1], env) == True:
return evaluate(ast[2], env)
if evaluate(ast[1], env) == False:
return evaluate(ast[3], env)
# Lists
if ast[0] == 'cons':
head = evaluate(ast[1], env)
tail = evaluate(ast[2], env)
return [head] + tail
if ast[0] == 'head':
eval_new_ast = evaluate(ast[1], env)
if eval_new_ast == []:
raise LispError
else:
return eval_new_ast[0]
if ast[0] == 'tail':
eval_new_ast = evaluate(ast[1], env)
if eval_new_ast == []:
raise LispError
else:
return eval_new_ast[1:]
if ast[0] == 'empty':
if evaluate(ast[1], env) == []:
return True
else:
return False
# Functions
if ast[0] == 'define':
assert_valid_definition(ast[1:])
symbol = ast[1]
value = evaluate(ast[2], env)
env.set(symbol, value)
return symbol
if ast[0] == 'lambda':
if len(ast) != 3:
raise LispError("Wrong number of arguments")
if not is_list(ast[1]):
raise LispError("Parameters are not in list-form")
else:
return Closure(env, ast[1], ast[2])
if is_closure(ast[0]):
closure = ast[0]
arguments = ast[1:]
if len(arguments) != len(closure.params):
errormessage = "wrong number of arguments, expected " + str(len(closure.params)) + " got " + str(len(arguments))
raise LispError(errormessage)
arguments = [evaluate(a, env) for a in arguments]
bindings = dict(zip(closure.params, arguments))
new_env = closure.env.extend(bindings)
return evaluate(closure.body, new_env)
if is_list(ast[0]) or is_symbol(ast[0]):
closure = evaluate(ast[0], env)
return evaluate([closure] + ast[1:], env)
else:
raise LispError("not a function")
else:
raise LispError
def do_math(ast, operator, env):
first = evaluate(ast[1], env)
second = evaluate(ast[2], env)
if not is_integer(first) or not is_integer(second):
raise LispError
return operator(first, second)
def evaluate(ast, env):
"""Evaluate an Abstract Syntax Tree in the specified environment."""
print ast, env.variables
# otherwise, it will be a function
op = ast[0]
args = ast[1:]
# Simple Evaluation
# quote evaluation
if op == "quote":
assert_exp_length(args, 1)
return evaluate(args[0], env)
# atom function
if op == "atom":
assert_exp_length(args, 1)
return is_atom(evaluate(args[0], env))
# arithematic evaluation
if op in ['+', '-', '*', '/', 'mod', '>']:
assert_exp_length(args, 2)
arg1 = evaluate(args[0], env)
arg2 = evaluate(args[1], env)
if not (is_integer(arg1) and is_integer(arg2)):
raise LispError("Arguments of arithmetic operator should be numbers")
return eval_arithmetic(op, arg1, arg2)
# define evaluation
if op == "define":
try:
assert_exp_length(args, 2)
except LispError:
raise LispError("Wrong number of arguments")
var_name = args[0]
var_value = evaluate(args[1], env)
if not is_symbol(var_name):
raise LispError("non-symbol: %s" % var_name)
env.set(var_name, var_value)
return var_name
# equal evaluation
if op == "eq":
eval_arg1 = evaluate(args[0], env)
eval_arg2 = evaluate(args[1], env)
return is_atom(eval_arg1) and is_atom(eval_arg2) and eval_arg1 == eval_arg2
# Complex Evaluation
# if evaluation
if op == "if":
assert_exp_length(args, 3)
eval_predicate = evaluate(args[0], env)
if eval_predicate:
return evaluate(args[1], env)
else:
return evaluate(args[2], env)
if op == 'lambda':
try:
assert_exp_length(args, 2)
except LispError:
raise LispError("number of arguments")
print len(args)
lambda_params = args[0]
lambda_body = args[1]
return Closure(env, lambda_params, lambda_body)
if is_closure(op):
closure = op
assert_exp_length(args, len(closure.params))
new_env = Environment(closure.env.variables.copy())
for n, param in enumerate(closure.params):
new_env.set(param, evaluate(args[n], new_env))
return evaluate(closure.body, new_env)
# fundamental
if is_symbol(ast):
print 'is_symbol'
try:
return evaluate(env.lookup(ast), env)
except:
if len(ast) == 1:
raise LispError("undefined: %s" % ast[0])
else:
raise LispError("not a function: %s" % ast[0])
if is_atom(ast):
print 'is_atom'
return ast
if is_list(ast):
print 'is_list'
return evaluate(map(lambda inner_ast: evaluate(inner_ast, env), ast), env)