String -> Tokens -> (AST)
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README.md

AstAst

                      sSSSSs
                saaAAA     Tttttts
               sa   tT  t  TT    tt
        saaaaaaA  t tT  t  TT     Ts
       sa  tt  T    tT  t  TT     Ts   
 - -  AaaaaaaAaaaaAAt     TsssssTs
         tT      t tSTSsssSTt tt
                 t tt       t tt
                st tt      st tt  
               S t tt     S t tt  
                st tt      st tt  
                 t tt       t tt
                 t tts      t tts
                 S tS s     S tS ss
                tsssstss   tsssstSSS

How To

String -> Ast::Tokens

So you have a string, eg:

an example String, lorem!

And you want to turn it into a set of tokens, for some reason, but can't be bothered messing around with strscan so instead use Ast::Tokeniser

string = "an example String, lorem!"

class StringTokens < Ast::Tokeniser

  # A rule uses a regular expression to match against the string given
  # if it matches a token is created with the name given, eg. +:article+
  rule :article, /an|a|the/
  rule :word,    /[a-z]+/
  rule :punct,   /,|\.|!/
  
  # A rule can be passed a block that then modifies the match and returns
  # something new in it's place, here we are removing the capital.
  rule :pronoun, /[A-Z][a-z]+/ do |i|
    i.downcase
  end
end

StringTokens.tokenise(string)
#=> #< [0] <:article, "an">, <:word, "example">, <:pronoun, "string">, <:punct, ",">, <:word, "lorem">, <:punct, "!"> >

Ast::Tokens -> Ast::Tree

Later.

Goals/Ideas

Now that it is possible to take a string and turn it into a set of tokens, I want to be able to take the tokens and turn them into a tree structure. This should be easy to write using a similar DSL to Tokeniser. See below for an idea on how this might be done, though of course when I start writing it, it will change a lot.

Ast::Ast

Imagine we have a string:

string = <<EOS
def method
  print 'hi'
end
EOS

Which becomes these tokens:

tokens #=> [:defn], [:id, 'method'], [:id, 'print'], [:string, 'Hi'], [:end]

We're looking for a tree like this:

tree #=> [:defn, 'method', [
  [:id, 'print', [
    [:string, 'Hi']
  ]]
]]

Then the class could look something like (something being the keyword):

class MyAst < Ast::Ast

  # create a defn token
  token :defn do
    [
      # start with :defn
      :defn,
      
      # get the name of method by reading next :id
      read_next(:id), # if not :id throw error
      
      # read rest of block, until the matching :end
      [read_until(:end)]
    ]
  end
  
  # allows you to use the name given in place of a list of token names
  group :literal, [:string, :integer, :float]
  # really just creates an array which responds to name given
  group :defined, [:print, :puts, :putc, :gets, :getc]
  
  token :id do |t, v|
    case v
    when 'method'
      v
    when :defined
      [:call, v, [read_next(:literal)]]
    else
      [t, v]
    end
  end
  
  token(:string) {|i| i } # not really necessary
end

Copyright

Copyright (c) 2010 Joshua Hawxwell. See LICENSE for details.