---Raul Miller wrote:
> Ian Gorse wrote:
> > I am just trying to understand tacit verbs more, and I set myself
> > little algorithms to experiment in J.
> > I am just trying to understand the individual steps
> > required to make a tacit verb out of such simple calculations.
>
> My first step usually involves constructing an executable
> example of the
> phrase I want to work with, and some representative data.
I think that is good advice - get a working explicit version first. If you can
shorten it to one line you can also use 13 : 'my explicit sentence' to find
some where to start.
As you get more familiar with tacit, you might want to start building them from
scratch. For me at least, this is not a linear process, but I'll try to
describe a general approach that (I think) I tend to follow.
Put simply- I start at the end and work from the middle outwards (that probably
doesn't make much sense!).
What I mean is that I ask myself what the last operation will be, that verb
then becomes the middle verb of a 3 verb train or fork. Then I ask myself what
the left and right arguments need to be and work out what the last operation
needs to be for each of those, ... repeat until done.
In the case of the explicit sentence:
(2*y) + y
The last operation is the +, it therefore forms the middle tine of the main
fork. Its right argument is simply y or the right argument to the tacit
expression. A verb whose result is its right argument is ], so that becomes
right-hand tine of the main fork. The left argument to the middle tine needs to
be 2*y or 2 times the right argument to the tacit expression. The verb for
multiplication is * and I can make a new verb "2 times" by using & to bond the
2 to * like this 2&* . I now have a fork that I think should do the job so I
don't have to continue the process.
2&* + ]
With the box display form selected (Edit|Configure|Display) I can now check
that I do indeed have a fork. Type the proposed tacit verb in the session and
press Enter.
2&* + ]
+-------+-+-+
|+-+-+-+|+|]|
||2|&|*|| | |
|+-+-+-+| | |
+-------+-+-+
Yep that looks like the fork I was trying to create. Next step, does it work!
To test I usually just surround the tacit with parentheses and then add a right
(and left) argument.
(2&* + ]) 10
30
Looks like it behaves as required. Now I can assign it to a name (don't need
the brackets anymore!):
t=: 2&* + ]
t 10
30
Done.
I find trying to explain something to someone else is a great way of learning
so thanks for indulging me!!
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