A Case of the MUMPS

The other day I learned a tiny bit about a programming language called MUMPS. To start with, I learned that there is a programming language and database called MUMPS. It stands for "Massachusetts General Hospital Utility Multi-Programming System" and apparently has a history stretching back to before the dawn of C, having been originally developed at Massachusetts's General Hospital in 1966 and 1967. But MUMPS isn't just a historical curiosity — it's still powering multiple major electronic health record systems. (1)

I learned about MUMPS in the usual way — someone posting a question about it on r/learnprogramming. The OP works in healthcare and was getting unexpected results from the justify function, which they were using like this $J(%X, 3, 0). They expected a whole number result, or possibly a float with a single digit of precision. But they were getting the result with some padding on it. I'm assuming it looked like this " num". Well, my initial inclination was to suppose that the second argument referred to padding, and suggest changing it to $J(%X, 0, 0) for a whole number, or $J(%X, 0, 1). For a float with one significant digit. This would coincide with some pretty standard usage in some other languages I know of:

// prints some_float with minimum with 3 and precision 1
printf("%f3.1", some_float)

And indeed, the OP mentioned this as a possible solution. But I decided to take the educated guesswork out of the equation and do the right thing — read the docs. And in fact it was quite easy to find the relevant documentation, and rather easy to read the documentation too:

Func:   $J[USTIFY]
Form:   $J(expr,int1[,int2])
Retn:   expr space padded on the left to a length of int1 characters.
        If int2 is specified, expr is first rounded to int2 decimal places.
Std:    Complies exactly
Eg:     $J("ABC",5) -> "  ABC"
        $J(.456,6,2) -> "  0.46"

Thus having established the accuracy of my guess, I returned to Reddit bearing the fruits of my research — and of course, citing my sources.

(1) Until recently including the US's Veteran's Administration (VA). source]