Add expression parsing

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/syn/token.rs

@@ -19,11 +19,18 @@ pub enum TokenKind {
     Comma,
 
     Eq,
+    BangEq,
+    EqEq,
+    LtEq,
+    GtEq,
+    Lt,
+    Gt,
     Arrow,
     Plus,
     Minus,
     Splat,
     FSlash,
+    Bang,
 }
 
 impl Display for TokenKind {
@@ -46,11 +53,18 @@ impl Display for TokenKind {
             Comma => "comma",
 
             Eq => "equals",
+            BangEq => "not equals",
+            EqEq => "double equals",
+            LtEq => "less than or equal to",
+            GtEq => "greater than or equal to",
+            Lt => "less than",
+            Gt => "greater than",
             Arrow => "arrow",
             Plus => "plus",
             Minus => "minus",
             Splat => "splat (or times)",
             FSlash => "fslash (or divide)",
+            Bang => "not",
         };
         Display::fmt(s, fmt)
     }