I can now parse one thing

src/main.rs

@@ -57,10 +57,11 @@ impl ReplState for InterpreterState {
 
 fn repl_handler(input: &str, state: &mut InterpreterState) -> String {
     if state.show_tokens {
-        format!("Tokens: {:?}", tokenize(input))
-    } else if state.show_parse{
-        format!("Parse: {:?}", parse(tokenize(input)))
-    } else {
-        format!("{:?}", parse(tokenize(input)))
+        println!("Tokens: {:?}", tokenize(input))
     }
+
+    if state.show_parse {
+        println!("Parse: {:?}", parse(tokenize(input)))
+    }
+    format!("{:?}", parse(tokenize(input)))
 }

src/parser.rs

@@ -1,13 +1,8 @@
+use std::iter::Peekable;
+use std::slice::Iter;
+
 use tokenizer::Token;
 
-/* grammar
-
-   expr : term ((PLUS|MIMUS) term)*
-   term : factor ((MUL | DIV) factor)*
-   factor  : NUM | LPAREN expr RPAREN
-
-*/
-
 #[derive(Debug)]
 enum AST {
     BinOp(Box<AST>, Box<AST>, Box<AST>),
@@ -22,9 +17,56 @@ pub struct ParseError {
 
 pub type ParseResult = Result<AST, ParseError>;
 
-pub fn parse(input: Vec<Token>) -> ParseResult {
-    let mut current_token: Token;
+/* grammar
 
-    return Err(ParseError { err: "error!".to_string() });
+   expr : term ((PLUS|MIMUS) term)*
+   term : factor ((MUL | DIV) factor)*
+   factor  : NUM | LPAREN expr RPAREN
+
+*/
+
+struct Parser<'a> {
+    tokens: Peekable<Iter<'a, Token>>
+}
+
+impl<'a> Parser<'a> {
+
+    fn parse(&mut self) -> ParseResult {
+        let r = self.expr();
+        match self.expect(Token::Separator) {
+            None => (),
+            Some(err) => return Err(err)
+        }
+        match self.expect(Token::EOF) {
+            None => (),
+            Some(err) => return Err(err)
+        }
+        r
+    }
+
+    fn expect(&mut self, expected: Token) -> Option<ParseError> {
+        match self.tokens.next() {
+            Some(next) if *next == expected => None,
+            Some(next) => {
+                let err = format!("Expected {:?} but got {:?}", expected, next);
+                Some(ParseError { err: err })
+            }
+            None => {
+                let err = format!("Expected {:?} but got end of input", expected);
+                Some(ParseError { err: err })
+            }
+        }
+    }
+
+    fn expr(&mut self) -> ParseResult {
+        self.tokens.next();
+        return Ok(AST::Number(5.0));
+    }
+}
+
+pub fn parse(input: Vec<Token>) -> ParseResult {
+    let mut iter = input.iter().peekable();
+    let mut parser = Parser { tokens: iter };
+    return parser.parse();
 }
 

src/tokenizer.rs

@@ -1,4 +1,4 @@
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, PartialEq)]
 pub enum Token {
     EOF,
     Separator,
@@ -36,7 +36,6 @@ pub fn tokenize(input: &str) -> Vec<Token> {
             ';' => true,
             '(' => true,
             ')' => true,
-            '.' => true,
             _ => false
         }
     }