|Paradigms||Multi-paradigm: procedural, imperative, structured|
|Designed by||Niklaus Wirth, Tony Hoare|
|Typing discipline||Static, strong|
ALGOL W is a programming language. It is based on a proposal for ALGOL X by Niklaus Wirth and Tony Hoare as a successor to ALGOL 60 in International Federation for Information Processing (IFIP) IFIP Working Group 2.1 on Algorithmic Languages and Calculi, which specified, maintains, and supports the languages ALGOL 60 and ALGOL 68. When the committee decided that the proposal was an insufficient advance over ALGOL 60, the proposal was published as A contribution to the development of ALGOL. After making small modifications to the language Wirth supervised a high quality implementation for the IBM System/360 at Stanford University that was widely distributed.
It represented a relatively conservative modification of ALGOL 60, adding string, bitstring, complex number and reference to record data types and call-by-result passing of parameters, introducing the
while statement, replacing
switch with the
case statement, and generally tightening up the language.
ALGOL W's syntax is built on a subset of the EBCDIC character encoding set. In ALGOL 60, reserved words are distinct lexical items, but in ALGOL W they are only sequences of characters, and do not need to be stropped. Reserved words and identifiers are separated by spaces. In these ways ALGOL W's syntax resembles that of Pascal and later languages.
Much of ALGOL W's semantics is defined grammatically:
⟨procedure identifier⟩is an identifier that has been defined by a procedure declaration, a
⟨label identifier⟩is an identifier that is being used as a goto label.
⟨τ function identifier⟩is the syntactic entity for a function that returns a value of type
τ, if an identifier has been declared as an integer function in the current scope then that is expanded to
⟨integer function identifier⟩.
⟨integer expression⟩ / ⟨integer expression⟩and
⟨real expression⟩ / ⟨real expression⟩are valid but distinct syntactic entities that represent expressions, but
⟨real expression⟩ DIV ⟨integer expression⟩(i.e., integer division performed on a floating-point value) is an invalid syntactic entity.
This demonstrates ALGOL W's record type facility.
RECORD PERSON ( STRING(20) NAME; INTEGER AGE; LOGICAL MALE; REFERENCE(PERSON) FATHER, MOTHER, YOUNGESTOFFSPRING, ELDERSIBLING ); REFERENCE(PERSON) PROCEDURE YOUNGESTUNCLE (REFERENCE(PERSON) R); BEGIN REFERENCE(PERSON) P, M; P := YOUNGESTOFFSPRING(FATHER(FATHER(R))); WHILE (P ¬= NULL) AND (¬ MALE(P)) OR (P = FATHER(R)) DO P := ELDERSIBLING(P); M := YOUNGESTOFFSPRING(MOTHER(MOTHER(R))); WHILE (M ¬= NULL) AND (¬ MALE(M)) DO M := ELDERSIBLING(M); IF P = NULL THEN M ELSE IF M = NULL THEN P ELSE IF AGE(P) < AGE(M) THEN P ELSE M END
The major part of ALGOL W, amounting to approximately 2,700 cards, was written in Wirth's PL360. An interface module for the IBM operating system (OS) in use (OS, DOS, MTS, ORVYL) was written in IBM assembly language, amounting to fewer than 250 cards. 
In an OS environment on a 360/67 with spooled input and output files, the compiler will recompile itself in about 25 seconds. The compiler is approximately 2700 card images. Thus, when the OS scheduler time is subtracted from the execution time given above, it is seen that the compiler runs at a speed in excess of 100 cards per second (for dense code).
In a DOS environment on a 360/30, the compiler is limited only by the speed of the card reader. The compiler has successfully recompiled itself on a 64K 360/30 at a rate of 1200 cards per minute (the speed of the card reader). This is impressive when compared to the time needed for the DOS Assembler to assemble the interface module which consists of under 250 cards. When the macro instructions are expanded, the DOS interface has 972 card images and the Assembler takes 15 minutes for the assembly.
Edited: 2021-06-18 18:11:11