Algol Language Constructs

Algol Language Constructs This is an outline of the Algol family of programming languages and the highly influential syntactical constructs that they first introduced. The ALGOrithmic Language was created as a high-level language whose purpose was to facilitate the writability of programs that perform scientific computations. Artifacts of the language are present in its descendants, some of which have enjoyed a more widespread use in recent times--well-known examples are C and Pascal. Successive versions and derivatives of the original Algol 58 language (previously referred to as IAL, the International Algebraic Language) helped to usher in the software engineering revolution called structured programming. Algol Dialects and Control Flow constructs Algol 60 Interestingly, Algol 60 permits labels as subroutine parameters; this allows a nested subroutine to jump to a caller-defined location. Enumeration-controlled loops are the primary means of achieving operation repitition. if-then-else Syntax if condition then statement else if condition then statement else if condition then statement ... else statement The term if-then-else denotes a selection statement created by John McCarthy (author of Lisp) that was included in the Revised Report on the Algorithmic Language Algol 60. The initial if statement notation was improved upon by later languages. Explicit termination is now often required as in the case of the END keyword in Modula-2. Selection semantics are also disambiguated by elsif forms featured by a large collection of popular contemporary languages including Perl. Algol 68 Algol 68's design approach emphasized orthogonality. For a more in-depth discussion of this programming language quality, refer to the compactness and orthogonality section in the modularity chapter of the Art of Unix Programming. expression-orientation This version of Algol allowed if-then-else statements to be nested in an expression. C uses the less orthogonal tertiary operator represented by ?: for embedded conditionals. Algol-W Algol-W is an Algol 60 derivative proposed by Niklaus Wirth. It is not too suprising that it reads like Pascal. This language was never officially accepted as an Algol successor. while loop Syntax while condition do statement Wirth's innovation of logically-controlled looping constructs is of particular significance. This loop writing style is emulated by a myriad of imperative programming languages.