PL/0: Білім беру тілі және компилятор құрастыру негіздері

Programming language
the programming language introduced by Niklaus Wirth
PL/0 is a programming language, intended as an educational programming language, that is similar to but much simpler than Pascal, a general purpose programming language. It serves as an example of how to construct a compiler. It was originally introduced in the book, Algorithms + Data Structures = Programs, by Niklaus Wirth in 1976. It features quite limited language constructs: there are no real numbers, very few basic arithmetic operations and no control flow constructs other than "if" and "while" blocks. While these limitations make writing real applications in this language impractical, it helps the compiler remain compact and simple.

The main article on compilers honours PL/0 for introducing several influential concepts (stepwise refinement, recursive descent parsing, EBNF, P code, T diagrams) to the field by educating students to use these concepts. Over the last 3 decades, most university courses on compiler construction that used PL/0 have followed Wirth strictly in employing these techniques (see references below). Some years ago university courses deviated from the course set by Wirth with the replacement of the classical recursive descent parsing technique by a (nonetheless classical) Unix like approach of employing lex and yacc. Only recently an implementation (PL/0 Language Tools) along this way has also combined modern concepts like object orientation and design patterns with a modern scripting language (Python), allowing students to consume the source text of the implementation in a contemporary programming style.

In December 1976, Wirth wrote a small booklet about compiler construction, containing the full source code of the PL/0 compiler. The syntax rules above were taken from this first edition of Wirth's book Compilerbau. In later editions of this book (under the influence of his ongoing research) Wirth changed the syntax of PL/0. He changed the spelling of keywords like const and procedure to uppercase. This change made PL/0 resemble Modula 2 more closely. At the same time, Wirth's friend and collaborator C. A. R. Hoare was working on his influential communicating sequential processes concept, which used the exclamation mark ! and the question mark ? to denote communication primitives. Wirth added both symbols to the PL/0 language, but he did not mention their semantics in the book.