Re: Generating a pretty AST with LPeg

[Fabien <fleutot+lua@...>]

If getting a robust AST is a means to an end rather than fun for the sake of it, I'd suggest that you look at Metalua:

• The AST generator is now packaged as a separate Rock. Te parser itself is compatible with Lua 5.2 (although the rockspec might claim otherwise);
• It's mature, deployed in several largely used projects;
• A lot of trial / error / feedback /improvement has gone in the definition of the exact AST format;
• It supports nice features such as good AST / source mapping, or access to metadata such as comments attached to nodes.

$ luarocks install metalua-parser --local
[...]
$ lua -l luarocks.loader

Lua 5.1.4  Copyright (C) 1994-2008 Lua.org, PUC-Rio

> mlc = require 'metalua.compiler'.new() -- parser

> pp  = require 'metalua.pprint' -- pretty-printer

> ast = mlc:src_to_ast [[ for i=1, 10 do print(i) end ]]

> pp.print(ast,{hide_hash=true,metalua_tag=true})

{ `Fornum{ `Id "i", `Number "1", `Number "10", { `Call{ `Id "print", `Id "i" } } } }

Even if your goal is to have fun with LPeg, I believe it's wise to stick with Metalua's AST definition, unless you've got a good reason: there are many fixed mistakes in it, which could avoid being repeated :)

A complete description of the AST format is available here: http://git.eclipse.org/c/koneki/org.eclipse.koneki.metalua.git/tree/README-parser.md