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c#antlr4visitor-pattern

How do I check if my assignment is using the right variable?

i'm using visitor from ANTLR4 to develop an interpreter in c#. in my grammar, i have a rule for looping and a rule for assignment as below:

for_stmt
: FOR  EACH  ID  IN  collection  DO NEWLINE+
         (block NEWLINE*)?
  END  FOR
;

set_stmt
:SET  ID '.' ID TO  arithExpr
;

block
: for_stmt
| set_stmt
;

inside the for loop, we can have set statements like this:

for each record in recordCollection do
    set record.name to 10
end for

the record used inside the set statement must be the same as the record used in the loop. how can i check this?

Solution

  • Your visitor can maintain a stack of variable definitions (scopes):

    • The visit method for for_stmt pushes the variable declarations onto the stack (and pops it after visiting the child nodes)
    • The visit method for set_stmt inspects the stack and throws a runtime exception if it cannot find the accessed id on the stack