Re: [Haskell-cafe] Explaining monads

On 14/08/07, Seth Gordon wrote:

Sebastian Sylvan wrote:

...

On 14/08/07, Dan Piponi wrote:

...

If I was one of your students and you said that monads are recipes I would immediately ask you where the monads are in my factorial program regardless of whether you had introduced one or two different analogies for recipes.

Why would you? I really don't see where you would get that idea? If I tell you that a function returns "a fruit", would you ask where the fruit in your factorial program is? Probably not. Why would you go off and take an analogy for monads and apply it to something completely different and still think the analogy holds? A function is *not* a recipe in this analogy, it's just a function (which you hopefully should've covered by the time you get to monads. Monadic values, and *only* monadic values (not functions!) are to be viewed as analogous to real world cooking recipes in this analogy. Functions shouldn't. If you start mixing things together it will get confused, so just don't!

As a mostly-newbie who is working on his own monad tutorial (bwah-hah-hah), I share Dan's confusion about your analogy.

Teacher: "Monads are like recipes."

Student: "Aren't functions like recipes, too?"

Teacher: "Well, yes, but we're talking about monads now, not functions."

Teacher: No, functions are like chefs. They do things to their input. Monads are like recipes, they don't *do* anything at all, they just represent an action, they need chefs to interpret them. -- Sebastian Sylvan +44(0)7857-300802 UIN: 44640862