Question

Could someone kindly explain the control structure in J (specifically For and While loops)?
Let’s say I have a=:1 and b=:10, and I want to add ‘1’ to ‘a’ using For/While loops till a < b.

So, usually it would be something like (in other languages)

for i= 1 to b   
a=a+1    
next i

or

while a<=b    
a=a+1    
end

Help please. I know it’s simple, but I can’t figure out how to do this in loops.

Also, I read up on something called “explicits”. For example:

foo=: 3 : 0
if. 1 do. wdinfo 'success' end.
)

What would the 3 and 0 denote?

Answer 1

Control structures must be used within an explicit definition.
The explicit definition link will explain what the “3” and “0” signify, but note that the following are equivalent.

myfunction=: 3 : 0
  NB. define function/verb here
) 

myfunction=: verb define
  NB. define function/verb here
) 

Here is an example of defining an explicit function/verb containing a for loop:

for_eg=: verb define
 a=. 3
 b=. 8
 for. i.b do.
   a=. a + 1
 end. 
 a
)

Here is an example of using that verb:

for_eg ''
11

The Jwiki contains a wiki page describing how to define a verb. Note the references at the bottom for more info.