Question

I am very new to J (learning it for fun) and I am trying to read data from keyboard. I have tried to make a tiny script which reads in a string and reverses it:

|.(1!:1 3)

When I run it, I get a rank error. (I’m using 1!:1 3 instead of defining a verb because codegolf…)
Is there a command that can check the rank of 1!:1 3?

Answer 1

That’s a common mistake with foreigns.

The definition for foreign 1!:1 doesn’t help, because it really reads:

1!:1 y      Read. y is a file name or a file number (produced by 1!:21); the 
result is a string of the file contents., e.g. 1!:1 <'abc.q'. The following 
values for y are also permitted:

1 read from the keyboard (does not work within a script)
3 read from standard input (stdin) 

And so replacing y with 3 should work, right? Well, not quite, because what you’re really giving as an argument in writing:

1!:1 3

is an array made of 1 3. Sort of like giving it:

1!:(1 3)

when you want:

1!:1 (3)

For code golf purposes, use a right bracket:

1!:1]3