Initial creation

Author: ligong

.gitignore

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+*~
+*.o
+test

README.txt

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+Simple scheme
+
+Scheme is known as maxwell of computer science.
+I always want to understand how it works.
+Finally, I find some time and write a simple scheme interpreter with C++.
+
+This interpreter supports special operator:
+define, lambda, if, cond, let, quote, assign.
+
+It also supports big number and tail recursion.
+
+Most SICP exercise can be written with it.
+See the example directory in source files.
+
+
+
+
+
+

sscheme.cc

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+
+void Repl(char* name, FILE* file)
+{
+  Environment env;
+  
+  // repl(read evaluate print loop)
+  for(;;) {
+    if (!name)
+      printf(">");
+    Exp* exp = Exp::Read(file);
+    if (exp == NULL)
+      break;
+    Value val = exp->Eval(&env);
+    if (!name)
+      val->Print();
+    delete exp;
+  }
+}
+
+// opaque expression
+class Exp
+{
+ public:
+  
+  virtual Value Eval(Environment*) = 0;
+  virtual ~Exp() { }
+  
+  static Exp* Read();
+  
+ private:
+  // Disallow explict/copy/assignment constructor
+  Exp();
+  Exp(const Exp&);
+  void operator=(const Exp&);
+};
+
+class SelfEvalExp: public Exp
+{
+ public:
+  SelfEvalExp(Value value):  value_(value) { }
+  virtual Value Eval(Environment*) { return value_; }
+  
+ private:
+  Value value_;
+};
+
+class VariableExp: public Exp
+{
+ public:
+  VariableExp(Variable var): var_(var) { }
+  virtual Value Eval(Environment*);
+ private:
+  Variable var_;
+};
+
+Value VariableExp::Eval(Environment* env)
+{
+  assert(env);
+  return env->Lookup(var_);
+}
+
+class QuoteExp: public Exp
+{
+ public:
+  QuoteExp(Exp* exp): quote_text_(exp) { }
+  virtual Value Eval(Environment*) {return Value(text_);}
+ private:
+  Exp* text_;
+};
+
+class LambdaExp: public Exp
+{
+ public:
+  LambdaExp(Arguments plist, Code code; Environment*);
+  virtual Value Eval(Environment*);
+ private:
+  Arguments plist_;
+  Code code_;
+  Environment* env_;
+};
+
+class IfExp: public Exp
+{
+ public:
+  virtual Value Eval(Environment*);
+};
+
+class CondExp: public Exp
+{
+ public:
+  virtual Value Eval(Environment*);
+};
+
+class AssignExp: public Exp
+{
+ public:
+  virutal Value Eval(Environment*);
+};
+
+class DefineExp: public Exp
+{
+ public:
+  virtual Value Eval(Environment*);
+};
+
+class BeginExp: public Exp
+{
+ public:
+  virtual Value Eval(Environment*);
+};
+
+class AppExp: public Exp
+{
+ public:
+  virtual Value Eval(Environment*);
+};
+  
+
+int main(int argc, char* argv[])
+{
+
+  for(int i = 1; i < argc; i++) {
+    FILE* file = fopen(argv[i],"r");
+    if (!file) {
+      fprintf(stderr,"%s fail to open %s(%s)\n", argv[0], argv[i], strerr(errno));
+      return EXIT_FAILURE;
+    } else {
+      Repl(argv[i],file);
+      fclose(file);
+    }
+  }
+  if (argc == 1) repl(NULL,stdin);
+
+  return EXIT_SUCCESS;
+}