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The ENVIRON and USING clauses.
These clauses are kind of the ''inverse'' of the '''#include''' found in the [[C|C programming language]], or '''import''' found in [[Python]]. The purpose of the ENVIRON mechanism is to allow a program source to be broken into manageable sized pieces. Note that it is only necessary to parse the shared source file once, unlike a '''#include''' found in the C programming language where the include file needs to be parsed for each source file that includes it.
= Example of ENVIRON clause =
A file called ''mylib.a68'':
BEGIN INT dim = 3; # a constant # INT a number := 120; # a variable # ENVIRON EXAMPLE1; MODE MATRIX = [dim, dim]REAL; # a type definition # MATRIX m1; a number := ENVIRON EXAMPLE2; print((a number)) END
= Example of USING clause =
A file called ''usemylib.a68'':
USING EXAMPLE2 FROM mylib BEGIN MATRIX m2; # example only # print((a number)); # declared in mylib.a68 # print((2 UPB m1)); # also declared in mylib.a68 # ENVIRON EXAMPLE3; # ENVIRONs can be nested # 666 END
== Restrictions to the language from the standard '''ALGOL 68''' ==
- no algol68 FLEX and variable length arrays.
- MODE STRING implemented without FLEX.
- The PAR parallel clause was not implemented.
- nonstandard transput.
A translator/compiler for ALGOL 68C was available for the PDP-10 and System/360 as well as a number of other computers.
- [http://hopl.murdoch.edu.au/showlanguage.prx?exp=667 Cambridge Algol 68: on the historical roster of computer languages] - includes 10+ publication references.
- [http://portal.acm.org/ft_gateway.cfm?id=807148&type=pdf A TRANSPORTATION OF ALGOL68C - PJ Gardner, University of Essex] - March 1977 (From 370 to DECsystem-10)