crystal/reader.cr

   1 require "./types"
   2
   3 class Reader
   4   def initialize(@tokens)
   5     @pos = 0
   6   end
   7
   8   def current_token
   9     @tokens[@pos] rescue nil
  10   end
  11
  12   def peek
  13     t = current_token
  14
  15     if t && t[0] == ';'
  16       @pos += 1
  17       peek
  18     else
  19       t
  20     end
  21   end
  22
  23   def next
  24     peek
  25   ensure
  26     @pos += 1
  27   end
  28 end
  29
  30 def tokenize(str)
  31   regex = /[\s,]*(~@|[\[\]{}()'`~^@]|"(?:\\.|[^\\"])*"|;.*|[^\s\[\]{}('"`,;)]*)/
  32   str.scan(regex).map{|m| m[1]}.reject(&.empty?)
  33 end
  34
  35 def read_str(str)
  36   r = Reader.new(tokenize(str))
  37   begin
  38     read_form r
  39   ensure
  40     unless r.peek.nil?
  41       raise "expected EOF, got #{r.peek.to_s}"
  42     end
  43   end
  44 end
  45
  46 def parse_error(msg)
  47   raise Mal::ParseException.new msg
  48 end
  49
  50 def read_sequence(reader, init, open, close)
  51   token = reader.next
  52   parse_error "expected '#{open}', got EOF" unless token
  53   parse_error "expected '#{open}', got #{token}" unless  token[0] == open
  54
  55   loop do
  56     token = reader.peek
  57     parse_error "expected '#{close}', got EOF" unless token
  58     break if token[0] == close
  59
  60     init << read_form reader
  61     reader.peek
  62   end
  63
  64   reader.next
  65   init
  66 end
  67
  68 def read_list(reader)
  69   read_sequence(reader, Mal::List.new, '(', ')')
  70 end
  71
  72 def read_vector(reader)
  73   read_sequence(reader, Mal::Vector.new, '[', ']')
  74 end
  75
  76 def read_atom(reader)
  77   token = reader.next
  78   parse_error "expected Atom but got EOF" unless token
  79
  80   case
  81   when token =~ /^-?\d+$/ then token.to_i
  82   when token == "true"    then true
  83   when token == "false"   then false
  84   when token == "nil"     then nil
  85   when token[0] == '"'    then token[1..-2].gsub(/\\"/, "\"")
  86   else                         Mal::Symbol.new token
  87   end
  88 end
  89
  90 def list_of(symname, reader)
  91   reader.next
  92   Mal::List.new << Mal::Symbol.new(symname) << read_form(reader)
  93 end
  94
  95 def read_form(reader) : Mal::Type
  96   token = reader.peek
  97
  98   parse_error "unexpected EOF" unless token
  99   parse_error "unexpected comment" if token[0] == ';'
 100
 101   case token
 102   when "("  then read_list reader
 103   when ")"  then parse_error "unexpected ')'"
 104   when "["  then read_vector reader
 105   when "]"  then parse_error "unexpected ']'"
 106   when "'"  then list_of("quote", reader)
 107   when "`"  then list_of("quasiquote", reader)
 108   when "~"  then list_of("unquote", reader)
 109   when "~@" then list_of("splice-unquote", reader)
 110   when "^"  then list_of("with-meta", reader)
 111   when "@"  then list_of("deref", reader)
 112   else read_atom reader
 113   end
 114 end
 115
 116 require "./printer"
 117 puts pr_str(read_str("[+ 1 2] ; bar"))