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+lexer.rs - source
+        
+    
+    
+        

+                                
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@@ -179,8 +185,32 @@
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-
-#[derive(Debug, PartialEq)]
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+
#[derive(Debug, PartialEq)]
 pub enum Token {
     Eof,
     Def,
@@ -188,6 +218,11 @@
     Identifier(String),
     Number(f64),
     Char(char),
+    If,
+    Then,
+    Else,
+    For,
+    In,
 }
 
 pub struct Lexer<I>
@@ -202,12 +237,12 @@
 where
     I: Iterator<Item = char>,
 {
-    pub fn new(mut input: I) -> Lexer<I> {
+    pub fn new(mut input: I) -> Lexer<I> {
         let last_char = input.next();
         Lexer { input, last_char }
     }
 
-    fn step(&mut self) -> Option<char> {
+    fn step(&mut self) -> Option<char> {
         self.last_char = self.input.next();
         self.last_char
     }
@@ -215,7 +250,7 @@
     /// Lex and return the next token.
     ///
     /// Implement `int gettok();` from the tutorial.
-    pub fn gettok(&mut self) -> Token {
+    pub fn gettok(&mut self) -> Token {
         // Eat up whitespaces.
         while matches!(self.last_char, Some(c) if c.is_ascii_whitespace()) {
             self.step();
@@ -242,21 +277,26 @@
             }
 
             match ident.as_ref() {
-                "def" => return Token::Def,
-                "extern" => return Token::Extern,
-                _ => {}
+                "def" => return Token::Def,
+                "extern" => return Token::Extern,
+                "if" => return Token::If,
+                "then" => return Token::Then,
+                "else" => return Token::Else,
+                "for" => return Token::For,
+                "in" => return Token::In,
+                _ => {}
             }
 
             return Token::Identifier(ident);
         }
 
         // Number: [0-9.]+
-        if last_char.is_ascii_digit() || last_char == '.' {
+        if last_char.is_ascii_digit() || last_char == '.' {
             let mut num = String::new();
             num.push(last_char);
 
             while let Some(c) = self.step() {
-                if c.is_ascii_digit() || c == '.' {
+                if c.is_ascii_digit() || c == '.' {
                     num.push(c)
                 } else {
                     break;
@@ -268,12 +308,12 @@
         }
 
         // Eat up comment.
-        if last_char == '#' {
+        if last_char == '#' {
             loop {
                 match self.step() {
-                    Some(c) if c == '\r' || c == '\n' => return self.gettok(),
-                    None => return Token::Eof,
-                    _ => { /* consume comment */ }
+                    Some(c) if c == '\r' || c == '\n' => return self.gettok(),
+                    None => return Token::Eof,
+                    _ => { /* consume comment */ }
                 }
             }
         }
@@ -360,8 +400,22 @@
         assert_eq!(Token::Identifier("c".into()), lex.gettok());
         assert_eq!(Token::Eof, lex.gettok());
     }
+
+    #[test]
+    fn test_ite() {
+        let mut lex = Lexer::new("if then else".chars());
+        assert_eq!(Token::If, lex.gettok());
+        assert_eq!(Token::Then, lex.gettok());
+        assert_eq!(Token::Else, lex.gettok());
+    }
+
+    #[test]
+    fn test_for() {
+        let mut lex = Lexer::new("for in".chars());
+        assert_eq!(Token::For, lex.gettok());
+        assert_eq!(Token::In, lex.gettok());
+    }
 }
-

-

-    
+
+