Ruby: step0, step1

1 files changed, 74 insertions, 0 deletions

diff --git a/ruby/reader.rb b/ruby/reader.rb
new file mode 100644
index 0000000..d224e9c
--- /dev/null
+++ b/ruby/reader.rb
@@ -0,0 +1,74 @@
+require "types"
+
+class Reader
+    def initialize(tokens)
+        @position = 0
+        @tokens = tokens
+    end
+    def peek
+        return @tokens[@position]
+    end
+    def next
+        @position += 1
+        return @tokens[@position-1]
+    end
+end
+
+
+def tokenize(str)
+    re = /[\s,]*(~@|[\[\]{}()'`~^@]|"(?:\\.|[^\\"])*"|;.*|[^\s\[\]{}('"`,;)]*)/
+    return str.scan(re).map{|m| m[0]}.select{|m| m != ""}
+end
+
+def parse_str(t)
+    return t[1..-2].gsub(/\\"/, "\"").gsub(/\\n/, "\n")
+end
+
+def read_atom(rdr)
+    token = rdr.next
+    return case token
+        when /^-?[0-9]+$/ then       token.to_i # integer
+        when /^-?[0-9][0-9.]*$/ then token.to_f # float
+        when /^"/ then               parse_str(token) # string
+        when "nil" then              nil
+        when "true" then             true
+        when "false" then            false
+        else                         token.to_sym # symbol
+    end
+end
+
+def read_list(rdr, klass, start="(", last =")")
+    ast = klass.new
+    token = rdr.next()
+    if token != start
+        raise "expected '" + start + "'"
+    end
+    while (token = rdr.peek) != last
+        if not token
+            raise "expected '" + last + "', got EOF"
+        end
+        ast.push(read_form(rdr))
+    end
+    rdr.next
+    return ast
+end
+
+def read_form(rdr)
+    token = rdr.peek
+    return case rdr.peek
+        when ";" then  nil
+        when "(" then  read_list(rdr, List, "(", ")")
+        when ")" then  raise "unexpected ')'"
+        when "[" then  read_list(rdr, Vector, "[", "]")
+        when "]" then  raise "unexpected ']'" 
+        when "{" then  raise "unexpected '{'" 
+        when "}" then  raise "unexpected '}'" 
+        else           read_atom(rdr)
+    end
+end
+
+def read_str(str)
+    tokens = tokenize(str)
+    return read_form(Reader.new(tokens))
+end
+