def evaluate(e, r, k):
if is_atom(e):
if is_symbol(e):
return evaluate_variable(e, r, k)
else:
return evaluate_quote(e, r, k)
else:
first = e.car
if first == 'quote':
return evaluate_quote(e.cadr, r, k)
elif first == 'if':
return evaluate_if(e.cadr, e.caddr, e.cadddr, r, k)
elif first == 'begin':
return evaluate_begin(e.cdr, r, k)
elif first == 'set!':
return evaluate_set(e.cadr, e.caddr, r, k)
elif first == 'lambda':
return evaluate_lambda(e.cadr, e.cddr, r, k)
elif first == 'catch':
return evaluate_catch(e.cadr, e.cddr, r, k)
elif first == 'throw':
return evaluate_throw(e.cadr, e.caddr, r, k)
elif first == 'block':
return evaluate_block(e.cadr, e.cddr, r, k)
elif first == 'return-from':
return evaluate_return_from(e.cadr, e.caddr, r, k)
elif first == 'unwind-protect':
return evaluate_unwind_protect(e.cadr, e.cddr, r, k)
else:
return evaluate_application(e.car, e.cdr, r, k)
def extend_env(env, names, values):
if is_pair(names) and is_pair(values):
return VariableEnv(extend_env(env, names.cdr, values.cdr), names.car,
values.car)
elif is_null(names) and is_null(values):
return env
elif is_symbol(names):
return VariableEnv(env, names, values)
else:
raise TypeError("Arity mismatch")
def extend(env, variables, values):
if is_pair(variables):
if is_pair(values):
return cons(cons(variables.car, values.car),
extend(env, variables.cdr, values.cdr))
else:
raise ValueError("Too few values")
elif is_null(variables):
if is_null(values):
return env
else:
raise ValueError("Too many values")
elif is_symbol(variables):
return cons(cons(variables, values), env)
else:
raise RuntimeError("Branch should be unreachable")
def evaluate(expr, env):
if is_atom(expr):
if is_symbol(expr):
return lookup(expr, env)
else:
return expr
else:
first = expr.car
if first == 'quote':
return expr.cadr
elif first == 'if':
if evaluate(expr.cadr, env):
return evaluate(expr.caddr, env)
else:
return evaluate(expr.cadddr, env)
elif first == 'begin':
return eprogn(expr.cdr, env)
elif first == 'set!':
return update(expr.cadr, env, evaluate(expr.caddr, env))
elif first == 'lambda':
return make_function(expr.cadr, expr.cddr, env)
else:
return invoke(evaluate(expr.car, env), evlis(expr.cdr, env))
