Primitive Scalar Functions

Abstract

One communicates with an APL system through a computer terminal. There is a keyboard much like that of an ordinary typewriter, through which the user gives instructions, and there is a display device permitting the user to see both what he has typed and what response the computer makes. Some terminals are indeed typewriters, and the input and the output appear typed on a roll of paper, which can be kept afterwards as a record of the proceedings. The printing is done by a typeball or other printing device, on a carrier that moves across the page to type a line. Other terminals show input and output on a cathode-ray tube (television screen). These have some advantages over printing terminals: output comes fast, and they are relatively inexpensive; but there is no record to take away; an auxiliary device must be used to obtain a permanent copy. All the illustrations for this book have been produced on a (quite slow) printing terminal with typeball, which yields the most legible record; and that is the kind of terminal that will be referred to.