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_if_statement(args, env):
evalPredicate = evaluate(args[0],env)
if not (is_boolean(evalPredicate)):
raise LispError('predicate must return boolean value')
if evalPredicate:
return evaluate(args[1], env)
else:
return evaluate(args[2], env)
def unparse(ast):
"""Turns an AST back into lisp program source"""
if is_boolean(ast):
return "#t" if ast else "#f"
elif is_list(ast):
if len(ast) > 0 and ast[0] == "quote":
return "'%s" % unparse(ast[1])
else:
return "(%s)" % " ".join([unparse(x) for x in ast])
else:
# integers or symbols (or lambdas)
return str(ast)
def unparse(ast):
"""Turns an AST back into lisp program source"""
if is_boolean(ast):
return 'True' if ast else 'False'
elif is_list(ast):
if len(ast) > 0 and ast[0] == "quote":
return "'%s" % unparse(ast[1])
else:
return "(%s)" % " ".join([unparse(x) for x in ast])
else:
# integers or symbols (or lambdas)
return str(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 assert_boolean(p, exp=None):
if not is_boolean(p):
msg = "Boolean required, got '%s'. " % unparse(p)
if exp is not None:
msg += "Offending expression: %s" % unparse(exp)
raise LispError(msg)
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 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")