State for eval

src/rukka_lang/mod.rs

@@ -4,10 +4,14 @@ use std::iter::Peekable;
 use std::vec::IntoIter;
 use std::str::Chars;
 
-pub struct Rukka { }
+pub struct EvaluatorState { }
+
+pub struct Rukka { 
+  state: EvaluatorState
+}
 
 impl Rukka {
-  pub fn new() -> Rukka { Rukka { } }
+  pub fn new() -> Rukka { Rukka { state: EvaluatorState::new() } }
 }
 
 impl ProgrammingLanguageInterface for Rukka {
@@ -30,7 +34,7 @@ impl ProgrammingLanguageInterface for Rukka {
     };
 
     let output_str: String = sexps.into_iter().enumerate().map(|(i, sexp)| {
-      match eval(sexp) {
+      match self.state.eval(sexp) {
         Ok(result) => format!("{}: {}", i, result.print()),
         Err(err) => format!("{} Error: {}", i, err),
       }
@@ -40,7 +44,10 @@ impl ProgrammingLanguageInterface for Rukka {
   }
 }
 
-fn eval(expr: Sexp) -> Result<Sexp, String> {
+
+impl EvaluatorState {
+  fn new() -> EvaluatorState { EvaluatorState { } }
+  fn eval(&mut self, expr: Sexp) -> Result<Sexp, String> {
     use self::Sexp::*; use self::AtomT::*;
     Ok(match expr {
       Atom(atom) => match atom {
@@ -50,6 +57,7 @@ fn eval(expr: Sexp) -> Result<Sexp, String> {
       },
       List(items) => unimplemented!(),
     })
+  }
 }
 
 fn read(input: &str) -> Result<Vec<Sexp>, String> {