How can I read one byte from stdin in Dyalog APL?

Question

I’m trying to make a terminal user interface in Dyalog APL and need a way to read a single byte of user input from stdin. How can I do this? In Python for example, you can use sys.stdin.read(1).

I’ve tried using ⍞, but that reads a whole line.

Answer 1

You can do this with ⎕ARBIN, which can be used like this:

[number of bytes to read] [tie number of file to read from] ⎕ARBIN [bytes to output before reading from input]

The number of bytes to read is 1, and there are no bytes to output (⍬). You can assign a tie number to stdin with ⎕NTIE.

stdin←'/dev/stdin' ⎕NTIE 0
byte←⊃1 stdin ⎕ARBIN ⍬

⎕ARBIN returns a numeric vector, so First (⊃) is used to get the byte as a scalar.