1 files changed, 58 insertions, 0 deletions
diff --git a/ruby/step2_eval.rb b/ruby/step2_eval.rb
new file mode 100644
index 0000000..9cbae24
--- /dev/null
+++ b/ruby/step2_eval.rb
@@ -0,0 +1,58 @@
+require "readline"
+require "types"
+require "reader"
+require "printer"
+
+# read
+def READ(str)
+    return read_str(str)
+end
+
+# eval
+def eval_ast(ast, env)
+    return case ast
+        when Symbol
+            raise "'" + ast.to_s + "' not found" if not env.key? ast
+            env[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
+    el = eval_ast(ast, env)
+    f = el[0]
+    return f[*el.drop(1)]
+end
+
+# print
+def PRINT(exp)
+    return _pr_str(exp, true)
+end
+
+# repl
+repl_env = {}
+REP = lambda {|str| PRINT(EVAL(READ(str), repl_env)) }
+
+repl_env[:+] = lambda {|a,b| a + b}
+repl_env[:-] = lambda {|a,b| a - b}
+repl_env[:*] = lambda {|a,b| a * b}
+repl_env[:/] = 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