Monadic Functions

[aaditmshah]

@theScottyJam

The use-case presented is to "flatten nested code caused by using monadic data types". The example solution presented is very similar to other functional languages, but I wonder if there's alternative syntax we could explore that might be more friendly for those who are less familiar with the scary "monad" word :).

I'm open to using friendlier keywords instead of monadic and yield. For example, after thinking for a while I came up with the keywords flat instead of monadic and map! instead of yield.

const foo = flat (x) => {
  const y = map! [x * 1, x * 2, x * 3];
  const z = map! [y + 1, y + 2, y + 3];
  return z;
};

Note: Since map is a commonly used identifier, I didn't want to make it a keyword. Hence, I put an exclamation mark after map to make the keyword map!. I like this because the exclamation mark denotes side effects, kind of like the command syntax proposed by @mlanza.

Anyway, these functions can be called flat functions, which is a lot friendlier than calling them monadic functions. In addition, monadic functions could imply "functions which have only one input", which could be confusing for beginners.

It also makes sense to use flat and map! because m.flatMap(f) should be equivalent to m.map(f).flat(). This should make it easier to explain to beginners and it should also make it easier to remember that map! m expressions de-sugar to m.flatMap method calls.

Flat functions allow you to use map! m expressions, and then they flatten the results.

@theScottyJam

The point is that, even though this classic monad-style syntax being presented is very common among functional languages, I'm not actually sure that that's the best way to solve the problem for a not-as-functional-language where many users aren't as familiar with the concept of a monad.

I don't buy that this syntax would be difficult for JavaScript programmers to learn for two reasons.

1. JavaScript programmers are already familiar with the async…await syntax, which is the same thing as flat…map! except that it's specialized for promises. An await p expression can be de-sugared to a p.then method call. Similarly, a map! m expression can be de-sugared to an m.flatMap method call. This shouldn't be too difficult for JavaScript programmers to grok.
2. JavaScript programmers don't need to understand the concept of a monad in order to use flat functions. They already know what the map method does, what the flat method does, and what the flatMap method does. We can explain the syntax using these three operations on arrays, without ever having to use the word "monad". And once they understand the syntax as it operates for arrays, then we can generalize and show that this syntax works for any data type whose values have a flatMap method.