[Jprogramming] More newbie tacit headscratching: Dyads (eg nPr)

[Roger Hui]

This advice is sound.  It brings to mind something as 
told to me by Ken, as told to Ken by Howard Aiken:  
A systems is made up of components; a component is 
something you understand.



----- Original Message -----
From: Don Guinn <donguinn at gmail.com>
Date: Thursday, February 11, 2010 18:59
Subject: Re: [Jprogramming] More newbie tacit headscratching: Dyads (eg nPr)
To: Programming forum <programming at jsoftware.com>

> With practice you will be able to build more complex definitions 
> tacitly;however, there are benefits to making the definition is 
> steps. Each step
> handling an easily understood thought. In your case you have 
> three steps,
> not too difficult to handle in one step, but can illustrate how 
> you can
> handle tacit definitions which are much more complex.
> 
> Take your three steps:
> 
>    nCr =: !~
>    n14Cr =: 14&nCr
>    n14Cr2=: ! * n14Cr
>    n14Cr2 3
> 2184
> 
> Looks like it works. But it still references all the definitions 
> of each
> step. There is an adverb f. (Fix) which substitutes primitives 
> for defined
> names.
> 
>    n14Cr2=: (! * n14Cr) f.
>    n14Cr2
> +-+-+------------+
> |!|*|+--+-+-----+|
> | | ||14|&|+-+-+||
> | | ||  | ||!|~|||
> | | ||  | |+-+-+||
> | | |+--+-+-----+|
> +-+-+------------+
> 
> Notice that now n14Cr2 is all primitives. The references were 
> removed. It
> still works.
> 
>    n14Cr2 3
> 2184
> 
> If you would like to see it in text form use 5!:5 to see it in 
> text form.
> 
>    5!:5<'n14Cr2'
> ! * 14&(!~)
> 
> This is not a very complex definition, but with this process you 
> can build
> extremely complex tacit definitions in many steps, each step 
> testable to
> verify its validity. And using the steps, debug at the step 
> level to find
> errors.