def _eval(self, expr, env):
if selfeval.is_self_evaluating(expr):
return expr
elif quote.is_quoted(expr):
return quote.text_of_quotation(expr)
elif definition.is_definition(expr):
return self._eval_definition(expr, env)
elif sequence.is_begin(expr):
return self._eval_sequence(sequence.begin_actions(expr), env)
elif binding.is_let_binding(expr):
return self._eval_binding(expr, env)
elif variable.is_variable(expr):
return lookup_variable_value(expr, env)
elif assignment.is_assignment(expr):
return self._eval_assignment(expr, env)
elif conditional.is_if(expr):
return self._eval_if(expr, env)
elif conditional.is_cond(expr):
return self._eval(conditional.cond_to_if(expr), env)
elif conditional.is_and(expr):
return self._eval_and(expr, env)
elif conditional.is_or(expr):
return self._eval_or(expr, env)
elif lambdaexpr.is_lambda(expr):
return procedure.make_procedure(
lambdaexpr.lambda_parameters(expr),
lambdaexpr.lambda_body(expr),
env)
elif procedure.is_application(expr):
return self._apply(
self._eval(procedure.operator(expr), env),
self._list_of_values(procedure.operands(expr), env))
def _eval_and(self, expr, env):
if procedure.no_operands(procedure.operands(expr)):
return Boolean(True)
def inner(expr, env):
if sequence.is_last_expr(expr):
return self._eval(sequence.first_expr(expr), env)
if not self._eval(sequence.first_expr(expr), env):
return Boolean(False)
return inner(sequence.rest_exprs(expr), env)
return inner(sequence.rest_exprs(expr), env)
def _eval_or(self, expr, env):
if procedure.no_operands(procedure.operands(expr)):
return Boolean(False)
def inner(expr, env):
if sequence.is_last_expr(expr):
return self._eval(sequence.first_expr(expr), env)
first_value = self._eval(sequence.first_expr(expr), env)
if first_value:
return first_value
return inner(sequence.rest_exprs(expr), env)
return inner(sequence.rest_exprs(expr), env)
