Grafting Functional Support on Top of an Imperative Language

[Lars Ivar Igesund]

Bill Baxter wrote:

> Lars Noschinski wrote:
>> * Jarrett Billingsley <kb3ctd2 at yahoo.com> [08-04-05 05:15]:
>>> I'm not one to be listened to, but I think the idea behind monads is
>>> to wrap an inherently impure action (like IO) in a functional shell.
>>> In an imperative language, you do something like:
>> 
>> Monads are an imperative sublanguage. IO Monads (which are the ones able
>> to do impure things) are safe, because there is no way to extract the
>> information wrapped in the monad.
>> 
>> So if you do a read, you don't get a "String", you get an "IO String"
>> (i.e. an IO monad containing a string). But you can apply functions to
>> the IO monad, which operate on the wrapped value and return a new IO
>> monad (for example a method parsing the String to an integer).
>> 
>> For the functional part of the program (all things outside of the IO
>> monad), the return value of e.g. readLine is always the same - an IO
>> monad representing the action of reading a line of input and therefore
>> it is pure.
> 
> Hmm, so would it be correct to say that monad is just another way to say
> 'impure function'?  It sounds like that's all you're saying.  So just
> like we're going to have 'pure' to isolate the functional code in D,
> functional languages have 'impure' functions that isolate the
> procedural/stateful stuff.  They just happen to give those impure
> functions a ridiculous name.
> 
> Seriously why on earth are they called 'monads'?  Sounds like it derives
> from "mono" meaning "one", like "triad" is a group of three things.  So
> 'monad' should mean a group of one thing I would thing.  Yet it means
> "impure function".  Really odd.  I hate it when people give things
> terrible non-descriptive names.  But maybe there's a rational
> explanantion?

I always thought it had to do with money, but then I'm not a native English
speaker ...

-- 
Lars Ivar Igesund
blog at http://larsivi.net
DSource, #d.tango & #D: larsivi
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