CorePascal.g4

grammar CorePascal;
parse : module ;

//--- parser -------------------------------------

module
    : modHeader
      block '.'
    ;

modHeader
    : 'module' IDEN ';'?
    ;

block
    : 'begin' ( statement ';' )* 'end'
    ;

statement
    : // pass
    ;

//--- scanner ------------------------------------

WHITESPACE
    : ('\u0000' .. '\u0020' )+  // space + all ascii control chars
        -> channel(HIDDEN)
    ;

IDEN
    : Alpha ( Alpha | Digit | '_' )*
    ;

fragment Alpha : 'a'..'z' | 'A'..'Z' ;
fragment Digit : '0'..'9' ;

hello.pas

module hello;
begin
end.

parsetree.txt

# export CLASSPATH=".:/path/to/antlr-4.0-complete.jar:$CLASSPATH"
# alias grun='java org.antlr.v4.runtime.misc.TestRig'


$ grun CorePascal parse -trace hellocore.pas
enter   parse, LT(1)=module
enter   module, LT(1)=module
enter   modHeader, LT(1)=module
consume [@0,0:5='module',<3>,1:0] rule modHeader alt=1
consume [@2,7:15='hellocore',<7>,1:7] rule modHeader alt=1
consume [@3,16:16=';',<4>,1:16] rule modHeader alt=1
exit    modHeader, LT(1)=begin
enter   block, LT(1)=begin
consume [@5,18:22='begin',<2>,2:0] rule block alt=1
consume [@7,24:26='end',<5>,3:0] rule block alt=1
exit    block, LT(1)=.
consume [@8,27:27='.',<1>,3:3] rule module alt=1
exit    module, LT(1)=<EOF>
exit    parse, LT(1)=<EOF>

$ grun CorePascal parse -tree hellocore.pas
(parse (module (modHeader module hellocore ;) (block begin end) .))