Elparser

A parser for S-expression of emacs lisp and some utilities.

require 'elparser'

parser = Elparser::Parser.new

 # list and literals
obj1 = parser.parse1("(1 2.3 a \"b\" () (c 'd))")

p obj1.to_ruby
 # => [1, 2.3, :a, "b", nil, [:c, [:d]]]


 # alist and hash
obj2 = parser.parse1("( (a . 1) (b . \"xxx\") (c 3 4) (\"d\" . \"e\"))")

p obj2.to_ruby
 # => [[:a, 1], [:b, "xxx"], [:c, 3, 4], ["d", "e"]] 

p obj2.to_h
 #  => {:a=>1, :b=>"xxx", :c=>[3, 4], "d"=>"e"} 

p Elparser::encode([1,1.2,-4,"xxx",:www,true,nil])
 # => "(1 1.2 -4 \"xxx\" www t nil)"
 
p Elparser::encode({:a => [1,2,3], :b => {:c => [4,5,6]}})
 # => "((a 1 2 3) (b (c 4 5 6)))"

Add this line to your application's Gemfile:

gem 'elparser'

And then execute:

$ bundle

Or install it yourself as:

$ gem install elparser

The class Elparser::Parser is parser for emacs-lisp S-expression. The user program creates an instance of the class and parses the S-exp string with parse1 method. If the source string has multiple S-expressions, one can use parse method.

If the Parser#parse1 method succeed in parsing the given S-exp string, it returns a SExp object which is AST of S-exp. Invoking to_ruby method of the SExp object, one can obtain a ruby object. Parser#parse method returns an array of SExp objects.

The SExp objects are instances of SExpXXX classes: SExpNumber, SExpString, SExpSymbol, SExpNil, SExpCons, SExpList, SExpListDot and SExpQuoted. Each classes represent corresponding S-exp objects.

If the given S-exp list is an alist, invoking SExpList#to_h method, a Hash object can be obtained.

The module method Elparser::encode encodes the ruby objects into elisp S-expressions. The another method Elparser::encode_multi receives an array of ruby objects and returns a S-expression string in which multiple S-expressions are concatenated.

If an object which is not defined in serialization rules is given, this method raises the exception StandardError with some messages. See the next section for the encoding detail.

The primitive objects are translated straightforwardly.

A quoted expression is translated to an array. Both nil and () are translated to nil. Cons cells and lists are translated to arrays.

The Array and Hash objects are translated to lists and alist respectively. Cons cells and quoted expressions can't be expressed by any Ruby object. If those S-expressions are needed, one can obtain such S-expressions with creating instances of SExpCons and SExpQuoted directly and calling the to_s method.

Copyright (c) 2015 SAKURAI Masashi Released under the MIT license