Various languages for talking to a computer

Press, 24 January 1984, Page 19

Various languages for talking to a computer

MARY MATTHEW continues her series on computer awareness. The cartoon is by RITA PARKINSON.

Everything you say to a computer has to be translated into machine language which it can “understand.”

Nowadays, the computer does this for you. With the first computers, you often had to enter instructions and data, one binary number at a time (Remember? R2D2 is 11010010 10110010 10111011 10110010 in the ASCII character code).

Rather than talk directly to a computer in unwieldy Base 2 notation, it saves humans time to use Base. 8 numbers (octal) or Base 16 numbers (hexadecimal) instead. In “hex,” R2D2 reads 52 32 44 32. A “converter program” changes these into binary code.

Even with these short cuts, it is almost impossible to write a long program in machine code, working out memory locations and calculating how many of them are needed for each instruction and for the data. It is too easy to make mistrakes — yes you can spot that one, but try proof-reading numbers for more than a few minutes.

The answer is assembly language. With this, the converter program is called an “assembler,” and the code is easier to read, since it uses alphabetical abbreviations

for instructions, memory locations and data.

A program •in the assembly language of a microcomputer might start off: LD DCO, ADDRI. Which means “load the address, ADDRI, into data counter register DCO, as a 16-bit binary data value.” Now you see why most people prefer to communicate with computers in a language rather “higher” than assembly language, even at the loss of some flexibility. The first widely-used higher-level language, developed in 1956, was FORTRAN (FORmula TRANslator). With only a few modifications, it is still going strong. FORTRAN is used mainly for science and engineering. It is a large language, with a huge library of mathematical and statistical routines.

A FORTRAN program is “compiled”; you enter the whole FORTRAN “source” program into the computer, then a program called a “compiler” translates it into an “object” program in machine language. The object program can be saved on tape or disk and runs very quickly. If you want to make any changes, you make them in FORTRAN to the source program, and compile a new object program. The FORTRAN language, together with its compiler and its huge library of statistical routines, takes up a good deal of computer memory and needs at least 128 K for number-crunching. As microcomputer memory becomes cheaper, technical programmers are demanding FORTRAN for their personal computers.

The year, 1960, was a great year for computer languages, with COBOL, ALGOL and LISP appearing. COBOL (COmmon Busi-ness-Oriented Language) was designed to do business data-processing, and has proved very powerful for operating elaborate filing systems. COBOL is more Englishlike in appearance than most other programming languages. For example, you write “is greater than” instead of the usual maths symbol Each program is separated into distinct divisions, which makes it self-docu-menting. Although COBOL was supposed to be “Common” to all computers using it, there are now several versions and it is no longer truly “machine-independ-ent.”

LINC, Christchurch’s own world-class software, generates COBOL source code which is then compiled, though this is not obvious to the user. COBOL is still the language used by the majority of commercial programmers.

ALGOL 60 (ALGOrithmic Language) developed from ALGOL 58, which was designed by an international committee, for problemsolving procedures (algorithms).

ALGOL 58 is memorable for two other offshoots, MAD and JOVIAL. ALGOL 60 was the first programming language to have a precisely defined set of grammatical rules, or syntax.

ALGOL, in its variety of forms, has not been as widely used as FORTRAN and COBOL, though it was popular in Europe.

ALGOL is a rather difficult language, and Pascal was developed originally to help students learn it. It has had a great effect on the development of other progamming languages. Until four years ago, ALGOL was the language of choice for scholarship applied maths candidates.

LISP (LISt Processing language) is the oldest computer language that does not seem obsolete to computer scientists.

symbols than doing number crunching, so languages like LISP are likely to be more use in the long run than FORTRAN, COBOL, BASIC, and Pascal for machines that “think.”

You sat up when I said “BASIC.” “LISP may be a language of the future,” I hear you say, “but what about now? BASIC is where my pocket is, if I get one of these home computers. Tell me more about BASIC.” Well, BASIC put in an appearance about four years after COBOL, ALGOL and LISP, and became so popular that is all you will be hearing about next time.

It was developed at M.I.T. from John McCarthy’s work on non-numeric computer language. LISP is the language of Artifical Intelligence, and as such, has had quite an airing lately in Douglas Hofstadter’s Metamagical Themas in “Scientific American.” Imagine a robot sitting on the grass, plucking the petals one by one from a daisy, and intoning: @ loves (she, me) ® not (loves (she, me)) © loves (she, me) ® not (loves (she, me)) . . . That’s LISP, that is. LISP is great for symbol manipulation. When we are thinking, we spend a lot more time manipulating

LISP programs are nothing but lists. They handle non-numeric information such as English sentences or computer programs, which can change a good deal in length and structure while the program is running.

LISP is used for things like linguistic analysis, pattern recognition, generating and verifying mathematical proofs, simulations of human problem-solving, storage and retrieval of information, and most typicaly, for programs which write and run other programs.