5 files changed, 159 insertions, 0 deletions
diff --git a/ruby/printer.rb b/ruby/printer.rb
new file mode 100644
index 0000000..2d46e07
--- /dev/null
+++ b/ruby/printer.rb
@@ -0,0 +1,23 @@
+require "types"
+
+def _pr_str(obj, print_readably=true)
+    _r = print_readably
+    return case obj
+        when List
+            "(" + obj.map{|x| _pr_str(x, _r)}.join(" ") + ")"
+        when Vector
+            "[" + obj.map{|x| _pr_str(x, _r)}.join(" ") + "]"
+        when String
+            if _r
+                "\"" + obj.gsub(/\\/, "\\\\") \
+                          .gsub(/"/, "\\\\\"") \
+                          .gsub(/\n/, "\\\\n") + "\""
+            else
+                obj
+            end
+        when nil
+            "nil"
+        else
+            obj.to_s
+    end
+end
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
+
diff --git a/ruby/step0_repl.rb b/ruby/step0_repl.rb
new file mode 100644
index 0000000..dd32b27
--- /dev/null
+++ b/ruby/step0_repl.rb
@@ -0,0 +1,25 @@
+require "readline"
+
+# read
+def READ(str)
+    return str
+end
+
+# eval
+def EVAL(ast, env)
+    return ast
+end
+
+# print
+def PRINT(exp)
+    return exp
+end
+
+# repl
+def REP(str)
+    return PRINT(EVAL(READ(str), {}))
+end
+
+while line = Readline.readline("user> ", true)
+    puts REP(line)
+end
diff --git a/ruby/step1_read_print.rb b/ruby/step1_read_print.rb
new file mode 100644
index 0000000..20dd450
--- /dev/null
+++ b/ruby/step1_read_print.rb
@@ -0,0 +1,32 @@
+require "readline"
+require "types"
+require "reader"
+require "printer"
+
+# read
+def READ(str)
+    return read_str(str)
+end
+
+# eval
+def EVAL(ast, env)
+    return ast
+end
+
+# print
+def PRINT(exp)
+    return _pr_str(exp, true)
+end
+
+# repl
+def REP(str)
+    return PRINT(EVAL(READ(str), {}))
+end
+
+while line = Readline.readline("user> ", true)
+    begin
+        puts REP(line)
+    rescue Exception => e
+        puts "Error: %{e}" 
+    end
+end
diff --git a/ruby/types.rb b/ruby/types.rb
new file mode 100644
index 0000000..a7ce285
--- /dev/null
+++ b/ruby/types.rb
@@ -0,0 +1,5 @@
+class List < Array
+end
+
+class Vector < Array
+end