def the_assignment(new_val, val_fail):
old_val = lookup_variable_value(var, env)
set_variable_value(var, new_val, env)
def restore_old_value(*args):
set_variable_value(var, old_val, env)
return continue_with(val_fail, *args)
return continue_with(succeed, S.OK, restore_old_value)
def the_assignment(environment):
set_variable_value(var, value_exec(environment), environment)
return S.OK
match_args(is_cond, is_environment),
lambda expression, environment:
(g.eval(cond_to_if(expression), environment)),
)
g.define_eval_handler(
match_args(is_let, is_environment),
lambda expression, environment:
(g.eval(let_to_combination(expression), environment)),
)
g.define_eval_handler(
match_args(is_assignment, is_environment),
lambda expression, environment: (set_variable_value(
assignment_variable(expression),
g.eval(assignment_value(expression), environment),
environment,
)),
)
g.define_eval_handler(
match_args(is_definition, is_environment),
lambda expression, environment: (define_variable(
definition_variable(expression),
g.eval(definition_value(expression), environment),
environment,
)),
)
# apply handlers
def restore_old_value(*args):
set_variable_value(var, old_val, env)
return continue_with(val_fail, *args)
def the_assignment(new_val, val_fail):
set_variable_value(var, new_val, env)
return continue_with(succeed, S.OK, val_fail)