From 5e6dee2f0935d7cbc21ce6990b805077c7928f5f Mon Sep 17 00:00:00 2001
From: Teddy <ted.sybil@gmail.com>
Date: Wed, 7 Aug 2013 22:32:07 +0800
Subject: added support for `eval`

---
 builtin.cpp | 29 ++++++++++++++++++++++++++++-
 builtin.h   | 15 +++++++++++++++
 eval.cpp    |  1 +
 3 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/builtin.cpp b/builtin.cpp
index e435c8c..d9cee5e 100644
--- a/builtin.cpp
+++ b/builtin.cpp
@@ -616,7 +616,7 @@ Cons *SpecialOptIf::call(ArgList *args, Environment * &envt,
         top_ptr += 2;
         // Undo pop and invoke again
         // static_cast because it's a call invocation
-        return static_cast<Cons*>(ret_addr->car)->next;
+        return TO_CONS(ret_addr->car)->next;
     }
 }
 
@@ -817,6 +817,33 @@ Cons *SpecialOptQuote::call(ArgList *args, Environment * &envt,
 
 string SpecialOptQuote::ext_repr() { return string("#<Builtin Macro: quote>"); }
 
+SpecialOptEval::SpecialOptEval() : SpecialOptObj("eval") {}
+
+void SpecialOptEval::prepare(Cons *pc) {
+    state = 0;
+}
+
+Cons *SpecialOptEval::call(ArgList *args, Environment * &envt, 
+        Continuation * &cont, FrameObj ** &top_ptr) {
+    if (args->cdr == empty_list ||
+        TO_CONS(args->cdr)->cdr != empty_list)
+        throw TokenError(name, RUN_ERR_WRONG_NUM_OF_ARGS);
+    Cons *ret_addr = static_cast<RetAddr*>(*top_ptr)->addr;
+    Cons *pc = static_cast<Cons*>(ret_addr->car);
+    if (state)
+    {
+        *top_ptr++ = TO_CONS(args->cdr)->car;
+        return ret_addr->next;          // Move to the next instruction
+    }
+    else
+    {
+        state = 1;
+        top_ptr += 2;
+        return TO_CONS(args->cdr);
+    }
+}
+
+string SpecialOptEval::ext_repr() { return string("#<Builtin Macro: eval>"); }
 
 BUILTIN_PROC_DEF(make_pair) {
     ARGS_EXACTLY_TWO;
diff --git a/builtin.h b/builtin.h
index b6585f3..be40b90 100644
--- a/builtin.h
+++ b/builtin.h
@@ -216,6 +216,21 @@ class SpecialOptQuote: public SpecialOptObj {
         string ext_repr();
 };
 
+/** @class SpecialOptEval
+ * The implementation of `eval` operator
+ */
+class SpecialOptEval: public SpecialOptObj {
+    private:
+        unsigned char state; /**< 0 for prepared, 1 for pre_called */
+    public:
+        SpecialOptEval();
+        void prepare(Cons *pc);
+        Cons *call(ArgList *args, Environment * &envt, 
+                    Continuation * &cont, FrameObj ** &top_ptr);
+
+        string ext_repr();
+};
+
 #define BUILTIN_PROC_DEF(func)\
     EvalObj *(func)(ArgList *args, const string &name)
 
diff --git a/eval.cpp b/eval.cpp
index f05eae0..85b9482 100644
--- a/eval.cpp
+++ b/eval.cpp
@@ -21,6 +21,7 @@ void Evaluator::add_builtin_routines() {
     ADD_ENTRY("define", new SpecialOptDefine());
     ADD_ENTRY("set!", new SpecialOptSet());
     ADD_ENTRY("quote", new SpecialOptQuote());
+    ADD_ENTRY("eval", new SpecialOptEval());
 
     ADD_BUILTIN_PROC("+", num_add);
     ADD_BUILTIN_PROC("-", num_sub);
-- 
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