MonadicFor annotation can generate NPE about soabase-halva HOT 7 CLOSED

This is what I have now. Is this the correct generated version?

// Auto generated from io.soabase.halva.comprehension.ReaderOptionalForFactory by Soabase io.soabase.halva.comprehension.MonadicFor annotation processor
package io.soabase.halva.comprehension;

import io.soabase.halva.any.AnyVal;
import java.lang.SuppressWarnings;
import java.util.function.Supplier;
import javax.annotation.Generated;

@Generated("io.soabase.halva.comprehension.MonadicFor")
public class ReaderOptionalFor<A> {
    private final MonadicForImpl<Reader> delegate;

    private ReaderOptionalFor(MonadicForImpl<Reader> delegate) {
        this.delegate = delegate;
    }

    public static <A> ReaderOptionalFor<A> start() {
        return new ReaderOptionalFor<A>(new MonadicForImpl<Reader>(new ReaderOptionalForFactory()));
    }

    public <MF_A, MF_B> ReaderOptionalFor<A> forComp(AnyVal<MF_B> any, Supplier<? extends Reader<MF_A, MF_B>> supplier) {
        delegate.forComp(any, supplier);
        return this;
    }

    @SuppressWarnings("unchecked")
    public <MF_A, MF_B> Reader<MF_A, MF_B> yield(Supplier<MF_B> supplier) {
        return delegate.yield(supplier);
    }

    public <R> ReaderOptionalFor<A> letComp(AnyVal<R> any, Supplier<R> supplier) {
        delegate.letComp(any, supplier);
        return this;
    }
}

from soabase-halva.

Yep that looks right, awesome thanks!

from soabase-halva.

Ah no sorry that was wrong, if needs to look like this: https://github.com/Alex-At-Home/halva-scalaz-examples/blob/master/src/test/java/person/alexp/halva/examples/ReaderOptionalFor2.java

ie if you specify a (single) inner type (and any number of template types) instead of leaving it untyped (eg Optional and A here) then you're declaring that you're composing Monads

from soabase-halva.

Hmm interesting, it appears that now if you have >1 generic type in your monad then you can't use the untyped version, eg

• public class OptionalForFactory implements MonadicForWrapper<Optional> { is fine because Optional only takes one type
• public class ReaderOptionalForFactory<A> implements MonadicForWrapper<Reader<A, Optional>> { is fine because both types are specified
• public class ReaderForFactory implements MonadicForWrapper<Reader> { now errors

The reason we specified no types was that the "monadic type" can change via the flatMap/for comprehension, eg Reader<String, Int> -> flatMap(a -> a.toString()) -> Reader<String, String>.

So you'd have to do something like:

• public class ReaderForFactory<A> implements MonadicForWrapper<Reader<A, ?>> { - which is a bit nasty because it becomes quite tricky to persuade the flatMap to compile - the old untyped expression was attractive even though it wasn't super type safe because it was nice and easy to override the flatMap/map, vs having to wrestle with Java type inference.
  • (you don't get any additional type safety after writing the for wrapper)

So I think it should be possible just to revert to the old logic for untyped multi-generic-type monads?

from soabase-halva.

If there is a way if making the `MonadicForWrapper fully type safe then I am all for it :)

eg you could try to do

• public class OptionalForFactory<T> implements MonadicForWrapper<Optional<T>> {
• public class ReaderForFactory<A, T> implements MonadicForWrapper<Reader<A, T>> {
• public class ReaderOptionalForFactory<A, T> implements MonadicForWrapper<Reader<A, Optional<T>>> {

and then the forComp would become (eg):

• ReaderForFactory<A, T2> forComp(Any<T2>, Supplier<T2>) (etc)

I think that will work fine, and it was just more trouble than it was worth in my example code that inspired your annotations, because I wasn't auto generating code or whatever

Or it works fine as is, with the 2 lines commented out from the last commit (I stuck a message in the linked commit) :)

from soabase-halva.

The behavior is now optional. Use @MonadicFor(applyParentTypeParameter = true) to get the enhanced behavior. This will allow you to choose how the generation is done. Let me know if this solves the issue.

from soabase-halva.

I'm going to close this as the original issue is dealt with. If you want more functionality open another issue.

from soabase-halva.