Panic jump in Go - usebox.net

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2022-06-22 08:00:05

It is fair to say that at this point I have stopped refreshing my knowledge of Go and I’m learning new things. Lots of them, actually; thanks to the toy programming language that I’m implementing.

I am following Crafting Interpreters as reference for the implementation of an interpreter for my language. The book is implementing the tree-walk interpreter in Java and it can use exceptions, but those aren’t available in Go (which is a shame, I generally prefer languages that support exceptions).

Because the way a tree-walk interpreter works, when the return in line 4 gets evaluated, the interpreter is a few functions deep:

In Java, going from the last point to the first one and return from there is quite simple because we have exceptions that will clear those function calls and take us to where we want to go –because we can catch the exception there–, but in Go we can’t do that. Instead we have panic and recover, and we can use them to do something similar –that I called panic jump, but that is probably not the technical name–.

So before we call fun.Call, that could “panic jump”, we set a handler for it that will check that the panic jump is the one we can handle (PanicJumpReturn) and set the return values of Interpreter.call.

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