This commit changes the model underlying parser variables used to store
match results and parse positions. Until now they were treated as a
stack, now they are thought of as registers. The actual behavior does
not change (yet), only the terminology.
More specifically, this commit:
* Changes parser variable names from |result0|, |result1|, etc. to
|r0|, |r1|, etc.
* Changes various internal names and comments to match the new model.
* Renames the |computeVarIndices| pass to |allocateRegisters|.
One stack is conceptually simpler, requires less code and will make a
transition to a register-based machine easier.
Note that the stack variables are now named a bit incorrectly
(|result0|, |result1|, etc. even when they store also parse positions).
I didn't bother with renaming because a transition to a register-based
machine will follow soon and the names will change anyway.
The speed/size impact is insignificant.
Speed impact
------------
Before: 839.05 kB/s
After: 839.67 kB/s
Difference: 0.07%
Size impact
-----------
Before: 949783 b
After: 961578 b
Difference: 1.24%
(Measured by /tools/impact with Node.js v0.6.18 on x86_64 GNU/Linux.)
This commit replaces all variable name computations in |computeVarNames|
and |computeParams| passes by computations of indices. The actual names
are computed later in the |generateCode| pass.
This change makes the code generator the only place that deals with the
actual variable names, making them easier to change for example.
The code generator code seems bit more complicated after the change, but
this complexity will pay off (and mostly disappear) later.
Places all code that does something with "action" AST nodes under code
handling "choice" nodes.
This ordering is logical because now all the node handling code matches
the sequence in which various node types usually appear when descending
through the AST tree.
PEG.js grammar rules are represented by |rule| nodes in the AST. Until
now, all such nodes had a |displayName| property which was either |null|
or stored rule's human-readable name. This commit gets rid of the
|displayName| property and starts representing rules with a
human-readable name using a new |named| node (a child of the |rule|
node).
This change simplifies code generation code a bit as tests for
|displayName| can be removed (see changes in generate-code.js). It also
separates different concerns from each other nicely.
David Majda