Category:PL/0
This programming language may be used to instruct a computer to perform a task.
| Lang tag(s): | pl0 |
|---|---|
| See Also: |
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PL/0 is an educational programming language. It was originally introduced in the book, Algorithms + Data Structures = Programs, by Niklaus Wirth in 1976. Wirth uses PL/0 as an example of how to construct a compiler.
Syntax
The syntax rules of PL/0 can be specified in EBNF as follows:
program = block "." ;
block = [ "const" ident "=" number {"," ident "=" number} ";"]
[ "var" ident {"," ident} ";"]
{ "procedure" ident ";" block ";" } statement ;
statement = [ ident ":=" expression | "call" ident
| "?" ident | "!" expression
| "begin" statement {";" statement } "end"
| "if" condition "then" statement
| "while" condition "do" statement ];
condition = "odd" expression |
expression ("="|"<>"|"<"|"<="|">"|">=") expression ;
expression = [ "+"|"-"] term { ("+"|"-") term};
term = factor {("*"|"/") factor};
factor = ident | number | "(" expression ")";
Wirth in his book presents the version without ? ("receive an integer value and assign it to the variable") and ! ("display a value of the expression") statements. Instead, this version displays values of the variables after changing them. So, the program:
var a, b;
begin
a := 0; b := 10;
while a < 5 do
begin
a := a + 1;
b := b - 1;
end
end.
gives the output:
0
10
1
9
2
8
3
7
4
6
5
5
Some versions use other statements for receiving and displaying data, usually read and write.
Due to typograhic conventions, Wirth uses non-ASCII symbols ≠, ≤, and ≥. Some versions use # for "not equal", [ for "less or equal", and ] for "greater or equal" respectively.
Some versions accept only upper-case letters or only lower-case letters in keywords and identifiers.
External links
- Wikipedia has an article about PL/0.
- PL/0 - Pascal for small machines
Pages in category "PL/0"
The following 25 pages are in this category, out of 25 total.