This is a novice problem (which arose from reading "Easy J" by Linda
Alvort
I think that I have it worked out but this is something (IMHO) that
possibly should be in a primer.
I have occasion to use what is called rms or root mean square (usually
applied to a wave form).
I can define root, mean and square and can do something like:
root mean square 1 2 1 2
or
%:(+/%#)*: 1 2 1 2 NB. in
immediate execution
1.58114 OK
A natural tendency equivalent to saying mean=: +/%#
is to try
rms=: %:(+/%#)*:
But rms 1 2 1 2 fails.
However rms=: 3: ' %:(+/%#)*:y' or rms=: 13: ' %:(+/%#)*:y'
is OK
and the latter is equivalent to
rms=:[:%:[:(+/%#)*: which works
Alternatively rms=:%:@:(+/%#)@:*: also works
It is obvious that either the capped fork (from use of 13: or use of @:
work and I see
the reasoning behind this- forcing a sequential " root after mean after
square".
Am I right in assuming that immediate execution of
%:(+/%#)*: y where y is explicitly entered
is treated as 3: or 13: ' %:(+/%#)*::y ' (explicitly in that the
*:y is the argument for mean(+/%#) whose value is the argument for %:
i.e. as in APL for which 'tacit' doesn't exist)
and rms=: %:(+/%#)*: as a tacit verb with no argument is parsed as a
fork rather than sequentially as desired and runs into never never land?
The classic example of 'mean=:+/%# as a verb is misleading in that the
example is a single fork, but trying to extend it
does need a flag as to the need to emphasize the parsing.
(+/%#) *: 1 2 1 2 works but msg =:(+/%#)*: doesn't work but
msg=:(+/%#)@:*: or msg=:[:(+/%#)*: do work
Don Kelly
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