[Jprogramming] [: vs @ or @:

[Tracy Harms]

I defined a simple "lettermap" verb three (very slightly) different ways:
 
   lm0=:(|:@,:@~.);=
   lm1=:(|:@:,:@:~.);=
   lm2=:([:([:|:,:)~.);=
   lm2 'Mississippi'
┌─┬─────────────────────┐
│M│1 0 0 0 0 0 0 0 0 0 0│
│i│0 1 0 0 1 0 0 1 0 0 1│
│s│0 0 1 1 0 1 1 0 0 0 0│
│p│0 0 0 0 0 0 0 0 1 1 0│
└─┴─────────────────────┘
   
What is unclear to me is how to think of rank when using cap. There is an internal rank difference between lm0 and lm1, which appears to be of no consequence here. I don't know whether lm2 corresponds exactly to lm0, lm1, or neither. Most importantly, I'm not sure how to approach thinking through the differences. (Although, I suspect that the place to start would be with a verb where the difference between @ and @: is material.)
 
Advice will be appreciated.