README.md

lua-parser

This is a Lua 5.3 parser written with LPegLabel that generates an AST in a format that is similar to the one specified by Metalua. The parser uses LPegLabel to provide more specific error messages.

Requirements

    lua >= 5.1
    lpeglabel >= 1.6.0

API

The package lua-parser has two modules: lua-parser.parser and lua-parser.pp.

The module lua-parser.parser implements the function parser.parse:

• parser.parse (subject, filename)

  Both subject and filename should be strings. It tries to parse subject and returns the AST in case of success. It returns nil plus an error message in case of error. In case of error, the parser uses the string filename to build an error message.

The module lua-parser.pp implements a pretty printer to the AST and a dump function:

• pp.tostring (ast)

  It converts the AST to a string and returns this string.

• pp.print (ast)

  It converts the AST to a string and prints this string.

• pp.dump (ast[, i])

  It dumps the AST to the screen. The parameter i sets the indentation level.

AST format

block: { stat* }

stat:
        `Do{ stat* }
      | `Set{ {lhs+} {expr+} }                    -- lhs1, lhs2... = e1, e2...
      | `While{ expr block }                      -- while e do b end
      | `Repeat{ block expr }                     -- repeat b until e
      | `If{ (expr block)+ block? }               -- if e1 then b1 [elseif e2 then b2] ... [else bn] end
      | `Fornum{ ident expr expr expr? block }    -- for ident = e, e[, e] do b end
      | `Forin{ {ident+} {expr+} block }          -- for i1, i2... in e1, e2... do b end
      | `Local{ {ident+} {expr+}? }               -- local i1, i2... = e1, e2...
      | `Localrec{ ident expr }                   -- only used for 'local function'
      | `Goto{ <string> }                         -- goto str
      | `Label{ <string> }                        -- ::str::
      | `Return{ <expr*> }                        -- return e1, e2...
      | `Break                                    -- break
      | apply

expr:
        `Nil
      | `Dots
      | `Boolean{ <boolean> }
      | `Number{ <number> }
      | `String{ <string> }
      | `Function{ { `Id{ <string> }* `Dots? } block }
      | `Table{ ( `Pair{ expr expr } | expr )* }
      | `Op{ opid expr expr? }
      | `Paren{ expr }       -- significant to cut multiple values returns
      | apply
      | lhs

apply:
         `Call{ expr expr* }
       | `Invoke{ expr `String{ <string> } expr* }

lhs: `Id{ <string> } | `Index{ expr expr }

opid:  -- includes additional operators from Lua 5.3 and all relational operators
        'add'  | 'sub' | 'mul'  | 'div'
      | 'idiv' | 'mod' | 'pow'  | 'concat'
      | 'band' | 'bor' | 'bxor' | 'shl' | 'shr'
      | 'eq'   | 'ne'  | 'lt'   | 'gt'  | 'le'   | 'ge'
      | 'and'  | 'or'  | 'unm'  | 'len' | 'bnot' | 'not'

Usage

Code example for parsing a string:

local parser = require "lua-parser.parser"
local pp = require "lua-parser.pp"

if #arg ~= 1 then
    print("Usage: parse.lua <string>")
    os.exit(1)
end

local ast, error_msg = parser.parse(arg[1], "example.lua")
if not ast then
    print(error_msg)
    os.exit(1)
end

pp.print(ast)
os.exit(0)

Running the above code example using a string without syntax error:

$ lua parse.lua "for i=1, 10 do print(i) end"
{ `Fornum{ `Id "i", `Number "1", `Number "10", { `Call{ `Id "print", `Id "i" } } } }

Running the above code example using a string with syntax error:

$ lua parse.lua "for i=1, 10 do print(i) "
example.lua:1:24: syntax error, expected 'end' to close the for loop