3.2.2. effect.do module¶
An imperative-looking notation for Effectful code.
See do()
.
-
effect.do.
do
(f)¶ A decorator which allows you to use
do
notation in your functions, for imperative-looking code:@do def foo(): thing = yield Effect(Constant(1)) yield do_return('the result was %r' % (thing,)) eff = foo() return eff.on(...)
@do
must decorate a generator function (not any other type of iterator). Any yielded values must either be Effects or the result of ado_return()
call. The result of a yielded Effect will be passed back into the generator as the result of theyield
expression. Yieldeddo_return()
values will provide the ultimate result of the Effect that is returned by the decorated function. Note thatdo_return()
is only necessary for Python 2 compatibility; return statements can be used directly in Python 3-only code.It’s important to note that any generator function decorated by
@do
will no longer return a generator, but instead it will return an Effect, which must be used just like any other Effect.Errors are also converted to normal exceptions:
@do def foo(): try: thing = yield Effect(Error(RuntimeError('foo'))) except RuntimeError: yield do_return('got a RuntimeError as expected')
(This decorator is named for Haskell’s
do
notation, which is similar in spirit).
-
effect.do.
do_return
(val)¶ Specify a return value for a @do function.
The result of this function must be yielded. e.g.:
@do def foo(): yield do_return('hello')
If you’re writing Python 3-only code, you don’t need to use this function, and can just use the return statement as normal.