Seven Obscure Languages in Seven Weeks

Performing Input and Output

In the spirit of other interpreted languages, APL is based on a REPL loop: read a command, evaluate it, print the results, and loop, making the simplest “Hello, world!” program trivial (the “Hello, world!” ​code​​​ is a joke!). However, implicit printing doesn’t work when the result is assigned to a variable. To force the printout, assign the result to the system variable ⎕ known as “quad.” (The box is really a box, not a placeholder for a missing character; see comment.) Non-incidentally, the variable looks like a screen or terminal window because it symbolizes your computer’s screen.

      A←10 ⍝ No printout
      A ⍝ Implicit printout
10
      ⎕←A←10 ⍝ Explicit printout
10

The last statement in the preceding ...