Language Implementation Patterns

Adding a New Type to Java

Java doesn’t have a built-in vector math type (java.util.Vector is not meant for mathematics and isn’t a built-in type). Let’s say we wanted to add type vec so that we can do things like this:

First, we need a strategy to execute this code. The easiest thing to do is to translate this down to raw Java. That means we have to figure out a mapping from input to output. Most of the input is pure Java, so we can just leave that stuff alone. The best way to change a few things and leave everything else alone is to “edit” the token stream (TokenRewriteStream if you’re using ANTLR). We know the start and stop tokens ([ and ]), so we can replace everything in between yielding ...