Where should I put a `condp` like function?

[Idan Arye]

On Thursday, 18 April 2013 at 13:04:19 UTC, Graham Fawcett wrote:
> On Sunday, 14 April 2013 at 23:52:37 UTC, Idan Arye wrote:
>>
>> Now, I've got it working(the example actually compiles and 
>> prints "less then 5"), and I want to make a pull request to 
>> put it in Phobos(because it's a useful function) but I don't 
>> really know where to put it. None of the existing modules 
>> seems fit, and I don't want to open a new module(std.monad?) 
>> for a single function.
>
> Nit-picky observation: there's nothing monadic about your 
> predSwitch function, it wouldn't belong in a 'std.monad' module.
>
> Best,
> Graham

A monad is "a structure that represents computations"(quote from 
Wikipedia). While the Turing machine branch(=the main branch) of 
computability theory quickly fell into the Turing tarpit and had 
to moved to pseudo-code, the Lambda calculus was expended using 
the traditional mathematical method of defining symbols that 
replace other symbols.

That's why when in the Turing machine branch you could just write 
`if ... then ... else ...` and it's okay because it's 
pseudo-code, in Lambda calculus you actually have an IFTHENELSE 
defined as a lambda expression. And so on with loops, exception 
handling, and even type definitions and input/output.

I find that `predSwitch` - a function that represents the 
`switch` idiom - perfectly fits into the definition of monads.