The Shape of Code

Having watched other blogs run themed Advent calendars, this year I have plucked up the courage to attempt my own based on programming languages in alphabetical order. The choice of languages covered will be governed by a mixture of my having used them, me thinking they are interesting in some way and for some letters not having many languages to write about.

Off we go…

A is for Algol 60, awk, ALGOL_68, Ada, APL and Assembler.

Over 50 years later its amazing how modern the Algol 60 report feels (some might complain about the lack of object oriented features, but we have to wait until 1967 for these to appear). Unlike Cobol and Fortran, from the same period, Algol is not generally known today, but it has probably been much more influential on what came after it. Randell and Russell’s “ALGOL 60 Implementation” from 1963 was the go to book for compiler writers until the Dragon book appeared in 1977.

AWK is my go to language for simple text processing. It’s one line at a time approach to handling input maps so well on to many real world problems, using a bigger language just feels like overkill.

Algol 68 was just as ground breaking as its earlier namesake. The Chomsky revolution in linguistics was in full swing, everything could be specified using syntax (that messy semantics stuff was tamed!), and programming languages had to get with it. Algol 68 was specified using a two-level grammar, one level of grammar specified syntax rules that were used to specify the second level syntax rules for actual source code (i.e., rules specifying rules). This two-level approach enabled many semantic requirements, on code, to be specified by syntactic rules, which was considered to be a good thing. The problem was language exponents loved to explain the wonderful syntactic goings on to all and sundry, and the language never spread beyond those who fell in love with two-level grammars (yes, your author was young once). One of those involved in early work on Algol 68 thought it such a monstrosity that he left and same up with a much simpler language, Pascal. A blast from Christmas’s past for those who miss pouring over line printer output.

Ada gets a mention because rather than get involved with writing an Ada compiler for somebody else I started my own company working first in Pascal and then C. I’m not sure if anybody yet understands the reasons behind Ada’s failure to become the widely used language that it was intended to be (enough money was thrown at it). Those involved pivoted and these days Ada is touted as somehow being ideal for use in safety-critical applications.

APL. The language that insists you write code that is the antithesis of readability. Despite the need for a special keyboard to write programs this language used to have a surprisingly large following (it was big in financial institutions where the ability to succinctly evaluate complex formula was demanded). The fact that it proved possible to compile APL convinced me that it was possible to write a compiler for any language.

Assembler. How could I not mention assembler?

Things to read

Informal introduction to Algol 68 by Lindsey and van der meulen, for those who find the language definition, A Revised Report on the Algorithmic Language ALGOL 68, a little brain scrambling.

Grammars for Programming Languages by J. Craig Cleaveland and Robert C. Uzgalis is a very readable introduction to two-level grammars.

Rationale for Design Ada Programming Language by J. Ichbiah J. Barnes is full of interesting insights.

Effective awk Programming: Universal Text Processing and Pattern Matching by Arnold Robbins, the 4th edition is out in two months 🙂

I have never read any really good APL books. Suggestions welcome.