The design of dead languages…

Once you are versed in a few languages, in principle you should be able to read any piece of code and decipher some idea of what it is doing. Take for example the following piece of code below. Obviously from the code you can quickly discern that it calculates Fibonacci numbers, but what happens in the code, and what language is it?

Firstly, don’t fret about the language, likely you have never seen it before… it is S-algol, short for St. Andrews Algol (a dialect of Algol 60). It doesn’t differ terribly from any other procedural language. The first part of the program revolves around the two phrases let and write. Obviously write is used for output. The use of let likely seems strange to many programmers. It basically “introduces” a variable, i.e. declares it with an initial value. Interestingly Swift uses let to assign constants. The while loop is fairly trivial (no parentheses, compound statement delineated by begin-end).

The rest of the program is pretty self-explanatory. There is an if-do statement, which uses = for equality, and relegates assignment to the classic := operator. Basically this program prints the first 42 Fibonacci numbers in a 6 column by 7 row format – the “‘n” outputs a newline after six columns. You’ll notice that semicolon is used, but only to separate two or more statements on a single line (that almost makes sense).

Once you know the basic control structures used in programming, it shouldn’t be that hard to decipher most pieces of code (languages like APL are an exception of course). Even dead languages have a tale to tell about their design, and what features could evolve into future languages. What would I choose from S-algol?

  • The use of the words reads and write is extremely intuitive – print always has associations with a physical printer. The reads function is quiet unique because it is used in the form x := reads , which does not require parameters.
  • The language uses dynamic typing, which is odd for a compiled language, however the language was designed to “deduce” the type from its declaration using let.
  • Strings are integral types (Yah!). String constants are easy to create: let s := “olympus” . The ++ operator can be used to concatenate strings.
  • Arrays are vectors, such that let x := vector 1::8 of 0 creates an 8-element integer array containing zeroes. very clean syntax. The use of the term vector is good because it builds on existing knowledge.

Negatives? The languages uses both = and := for assignment in vectors to distinguish between constants and variables. This seems kind-of vague from the examples I have seen, and could lead to confusion.

P.S. If you want to play with the S-algol compiler you can find the sourse code here.


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