GNU Modula-2 supported dialects#
This section describes the dialects understood by GNU Modula-2. It also describes the differences between the dialects and any command line switches which determine dialect behaviour.
The GNU Modula-2 compiler is compliant with four dialects of Modula-2. The language as defined in ‘Programming in Modula-2’ 2nd Edition, Springer Verlag, 1982, 1983 by Niklaus Wirth (PIM2), ‘Programming in Modula-2’, 3rd Corrected Edition, Springer Verlag, 1985 (PIM3) and ‘Programming in Modula-2’, 4th Edition, Springer Verlag, 1988 (PIM4) http://freepages.modula2.org/report4/modula-2.html and the ISO Modula-2 language as defined in ISO/IEC Information technology - programming languages - part 1: Modula-2 Language, ISO/IEC 10514-1 (1996) (ISO).
The command line switches -fpim2, -fpim3, -fpim4
and -fiso can be used to force mutually exclusive
features. However by default the compiler will not aggressively fail
if a non mutually exclusive feature is used from another dialect. For
example it is possible to specify -fpim2 and still utilise
DEFINITION MODULES which have no export list.
Some dialect differences will force a compile time error, for example
in PIM2 the user must IMPORT SIZE from the module
SYSTEM, whereas in PIM3 and PIM4 SIZE is a pervasive
function. Thus compiling PIM4 source code with the -fpim2
switch will cause a compile time error. This can be fixed quickly
with an additional IMPORT or alternatively by compiling with
the -fpim4 switch.
However there are some very important differences between the dialects which are mutually exclusive and therefore it is vital that users choose the dialects with care when these language features are used.