2 files changed, 98 insertions, 0 deletions
diff --git a/ruby/env.rb b/ruby/env.rb
new file mode 100644
index 0000000..dfd5ec9
--- /dev/null
+++ b/ruby/env.rb
@@ -0,0 +1,28 @@
+class Env
+    attr_accessor :data
+    def initialize(outer=nil, binds=[], exprs=[])
+        @data = {}
+        @outer = outer
+    end
+
+    def find(key)
+        if @data.key? key
+            return self
+        elsif @outer
+            return @outer.find(key)
+        else
+            return nil
+        end
+    end
+
+    def set(key, value)
+        @data[key] = value
+        return value
+    end
+
+    def get(key)
+        env = find(key)
+        raise "'" + key.to_s + "' not found" if not env
+        env.data[key]
+    end
+end
diff --git a/ruby/step3_env.rb b/ruby/step3_env.rb
new file mode 100644
index 0000000..97be81d
--- /dev/null
+++ b/ruby/step3_env.rb
@@ -0,0 +1,70 @@
+require "readline"
+require "types"
+require "reader"
+require "printer"
+require "env"
+
+# read
+def READ(str)
+    return read_str(str)
+end
+
+# eval
+def eval_ast(ast, env)
+    return case ast
+        when Symbol
+            env.get(ast)
+        when List   
+            List.new ast.map{|a| EVAL(a, env)}
+        when Vector
+            Vector.new ast.map{|a| EVAL(a, env)}
+        else 
+            ast
+    end
+end
+
+def EVAL(ast, env)
+    if not ast.is_a? List
+        return eval_ast(ast, env)
+    end
+
+    # apply list
+    a0,a1,a2,a3 = ast
+    case a0
+    when :"def!"
+        return env.set(a1, EVAL(a2, env))
+    when :"let*"
+        let_env = Env.new(env)
+        
+        a1.each_slice(2) {|a,e| let_env.set(a, EVAL(e, let_env))}
+        return EVAL(a2, let_env)
+    else
+        el = eval_ast(ast, env)
+        f = el[0]
+        return f[*el.drop(1)]
+    end
+end
+
+# print
+def PRINT(exp)
+    return _pr_str(exp, true)
+end
+
+# repl
+repl_env = Env.new
+REP = lambda {|str| PRINT(EVAL(READ(str), repl_env)) }
+_ref = lambda {|k,v| repl_env.set(k, v) }
+
+_ref[:+, lambda {|a,b| a + b}]
+_ref[:-, lambda {|a,b| a - b}]
+_ref[:*, lambda {|a,b| a * b}]
+_ref[:/, lambda {|a,b| a / b}]
+
+while line = Readline.readline("user> ", true)
+    begin
+        puts REP[line]
+    rescue Exception => e
+        puts "Error: #{e}" 
+        puts "\t#{e.backtrace.join("\n\t")}"
+    end
+end