Re: [Haskell-cafe] Explaining monads

On 14/08/07, Dan Piponi wrote:

On 8/14/07, Sebastian Sylvan wrote:

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On 14/08/07, Dan Piponi wrote:

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Where do monads come in?

Well I would try to distinguish between code that we write to compute values, and values which represent monadic actions when coming up with analogies.

How would you make that distinction?

How can you *not* make a distinction? If you view source code as recipes, that's fine, but the *code* doesn't even exist in the program! You can't pass *code* around (unless you do it as String). Clearly there's a gulf of difference between the source code ASCII string that represent the factorial function, and a first class value that represents an action *in* the language.

At this point I can imagine students immediately thinking that my factorial program is a recipe and wondering why it doesn't involve monads.

Well that's easy, don't use the recipe analogy to explain code, use it for monadic values exclusively, and you avoid the confusion entirely! I don't think it's that complicated. Monads have a monadic type. They represent an abstract form of an "action", which can be viewed as an analogy to real-world cooking recipes. As long as you don't deliberately confuse things by using the same analogy for two different things I don't see where confusion would set in. -- Sebastian Sylvan +44(0)7857-300802 UIN: 44640862