grammar files .g compatibility frome Antlr 2.7 to 4?

Question

The situation: We are porting our old simulation platform for math/physics/CS popularization MobiNet from C++ to online JS. At that time the MobiNet language was dealt using Antlr 2.7.3.

• Can we expect our calc.g to directly work in Antlr4? (I'm afraid by the suffix renamed .g4).
• If not direct, how hard will it be to upgrade?
• If it will be difficult, is there any way to ease the job (e.g. with an older Antlr version, as long as the JS target works) ?

Note: We have no energy for re-design, just porting, and already many aspects to deal with.

Answer 1

Q1: As Lex also pointed out, no, the original grammar won't work.

Q2: Upgrading from ANTLR 2 to ANTLR 4 can be a tedious task depending on lots of small details. In your calc.g, the parser rules do not seem to be so complex, but you have to know that the concepts of the parsing technology changed from ANTLR 2 to ANTLR 3 (LL(k) to LL(*), see details here) and also from ANTLR 3 to ANTLR 4 (LL(*) to AdaptiveLL(*), details here). If you use the AST generation, it has changed a lot too. Also, you'll have to change the target from C++ and rewrite the actions anyway.

Q3: Upgrading from ANTLR 2 to ANTLR 3 is probably easier and might solve your migration issue. But it is another question if it's really worth spending time on upgrading to ANTLR 3 (and then, maybe, upgrade to another version later), or spending some (probably more) time on upgrading directly to ANTLR 4.