APL2 Packages: a Cautionary Tale

Transcribed from the printed issue; not yet reviewed. Read it in the PDF of the issue, page 100

The following cautionary tale, relating to the use of packaged workspaces in APL2, may cause readers some amusement.

On 3rd November I made some modifications to a workspace and saved it. A few days later one of my users came to me to complain that the date appearing on the printout produced by the program was incorrect, although the data were up to date. The date being printed was 3rd November.

A quick examination revealed that the date was put in the output from an object named TODAY — but this object was not a variable set by the program, rather, it was a function, and a packaged function at that. Examination of the listing for this function revealed all: function TODAY looks to see if a variable Today exists and if it does then the value of Today is returned; otherwise Today is set to the current date and that is the value returned. (I guess that it was written like that to facilitate the production of a report with a given date.) When I saved the modified workspace, the value of Today was saved with it. What I should have done next (see my article in Vector 7.2) was to )CLEAR, )COPY the workspace, reset the latent expression, name the workspace, then )SAVE again. Simple enough, I suppose, but easy to forget when one’s attention is distracted.

Nicholas Small