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The first stage in the compilation pipeline is the Ruby Parser. The Ruby parser receives either a String of code or a file and passes an AST to the next stage of the process, the generator.
The parser itself (called Melbourne) has a C part, which is essentially MRI’s parser, and a Ruby part, which is responsible for creating the Ruby AST. The C parser communicates with Ruby by calling a method for each node in the parse tree.
Each of these methods has a signature containing all of the information
about the part of the parse tree it is processing. For instance, if the
underlying Ruby code has an
if statement, the C parser will call
process_if with the line number, a parameter representing the
condition, and parameters representing the body of the if statement and
the else section, if any.
def process_if(line, cond, body, else_body) AST::If.new line, cond, body, else_body end
You can see all of the possible
process_ calls by taking a look at
lib/melbourne/processor.rb in the Rubinius source code.
Note that in many cases, the parser passes the result of calling a
process_ method as the arguments to a
process_ method. In
the case of
true if 1, the parser first calls
process_lit(line 1) and
process_true(line). It also calls
process_nil(line), because the
original parse tree contains a
nil for the
else body. It then calls
process_if with the line number, the result of
process_true, and the result of
This process recursively builds up a tree structure, which Rubinius passes on to the next stage, the Generator stage.
process_, which the C parser calls for each node in the raw parse tree.
There are two ways to customize this stage of the compilation process. The easiest way to customize the creation of the AST is through AST Transforms.
You can also subclass the Melbourne processor and define your own
handlers for the
process_ methods. This is an advanced topic that is
not yet documented.