Type checking and compilation

[travispaxton]

I’ve been reading through your docs and looking through the source code. How are you handing type checking? Are you deferring to Java? I see you have a list of op codes and it looks like there’s some Java code that is emitting them, but I’m not quite grasping how you’re compiling.

[cpurdy]

Hi Travis -

No, we're not deferring to Java for type checking. When we compile, we produce a record of each type, called a TypeConstant, and that is used for type checking. It's a huge pile of information (including a tree of sub-classes of TypeConstant, and a separate structure produced from TypeConstant called TypeInfo).

The type checking looks like this in IfStatement, where it knows it needs a condition to be a boolean, for example. I gave that as a super simple example, because most type checking is dramatically more complex than that, but it's mostly implemented in the validation stage of the compiler, by the various AST nodes.