ANTLR 'or' regular expression - parsing

Question

I have a serious problem about | expression.
My grammar contains expression like this.
...ifelse : 'IF' condition 'THEN' dosomething+ 'ENDIF'
...dosomething : assign | print | input;
but dosomething becomes constant. For example :
IF a > 3 THEN
PRINT "HEllo"
b = a
ENDIF
so first dosomething is print and grammar can't read assing, input.
If statements become like this, it works correct
IF a > 3 THEN
PRINT "HEllo"
PRINT myName
ENDIF
So i mean 'or' ( | | )+ expression becomes constants same as first occured expression.
grammar hellog;
prog : command+;
command : maincommand
| expressioncommand
| flowcommand
;
//main
maincommand : printcommand
| inputcommand
;
printcommand : 'PRINT' (IDINT | IDSTR | STRING) NL
| 'PRINT' (IDINT | IDSTR | STRING) (',' (IDINT | IDSTR | STRING))* NL
;
inputcommand : 'INPUT' (IDINT | IDSTR) NL
| 'INPUT' STRING? (IDINT | IDSTR) NL
;
//expression
expressioncommand : intexpression
| strexpression
;
intexpression : IDINT '=' (IDINT | INT) NL
| IDINT '=' (IDINT | INT) (OPERATORMATH (IDINT | INT))* NL
;
strexpression : IDSTR '=' (IDSTR | STRING) NL
| IDSTR '=' (IDSTR | STRING) ('+' (IDSTR | STRING))* NL
;
//flow
flowcommand : ifelseflow
| whileflow
;
ifelseflow : 'IF' conditionflow 'THEN' NL dosomething+ ('ELSEIF' conditionflow 'THEN' NL dosomething+)* ('ELSE' NL dosomething+)? 'ENDIF' NL;
whileflow : 'WHILE' conditionflow NL (dosomething)+ 'WEND' NL;
dosomething : command;
conditionflow : (INT | IDINT) OPERATORBOOL (INT | IDINT)
| (STRING | IDSTR) '=' (STRING | IDSTR)
;
INT : [0-9]+;
STRING : '"' .*? '"';
IDINT : [a-zA-Z]+;
IDSTR : [a-zA-Z]+'$';
NL : '\n';
WS : [ \t\r]+ -> skip;
OPERATORMATH : '+' | '-' | '*' | '/';
OPERATORBOOL : '=' | '>' | '<' | '>=' | '<=';
I just need a grammar to run these expression:
PRINT "Your name"
INPUT name
PRINT "HELLO" name
a = 6
IF a > 3 THEN
PRINT a
a = a -1
END IF
WHILE b = 3
PRINT b
a = b
WEND

Answer 1

My answer isn't exactly about the | alternatives, but please keep reading, because like you, I found implementation of if..else constructs in a BASIC-like language a real challenge to implement. I found some good resources online. When I got it right, many, many problems disappeared all at once and it just started to work. Please take a look at my grammar snip:
ifstmt
: IF condition_block (ELSE IF condition_block)* (ELSE stmt_block)?
;
condition_block
: expr stmt_block
;
stmt_block
: OBRACE statement+ CBRACE
| statement
;
And my implementation (in C# visitor pattern):
public override MuValue VisitIfstmt(LISBASICParser.IfstmtContext context)
{
LISBASICParser.Condition_blockContext[] conditions = context.condition_block();
bool evaluatedBlock = false;
foreach (LISBASICParser.Condition_blockContext condition in conditions)
{
MuValue evaluated = Visit(condition.expr());
if (evaluated.AsBoolean())
{
evaluatedBlock = true;
Visit(condition.stmt_block());
break;
}
}
if (!evaluatedBlock && context.stmt_block() != null)
{
Visit(context.stmt_block());
}
return MuValue.Void;
}
Much borrowed from Bart Kiers's excellent implementation of his Mu demonstration language. Lots of great ideas in that project of his. It really showed me the light and this code I've shown handles if statements great, nested arbitrarily deep if you need that. This is production code running a critical domain-specific language.