const tokenization

edn/src/edn_token.rs

@@ -10,11 +10,12 @@ pub enum Token<'a> {
 }
 
 impl<'a> Token<'a> {
-    pub fn chomp (source: &'a str) -> Result<(&'a str, Self), ParseError> {
+    pub const fn chomp (source: &'a str) -> Result<(&'a str, Self), ParseError> {
         use Token::*;
         use konst::string::{split_at, char_indices};
         let mut state = Self::Nil;
-        for (index, c) in source.char_indices() {
+        let mut chars = char_indices(source);
+        while let Some(((index, c), next)) = chars.next() {
             state = match state {
                 // must begin expression
                 Nil => match c {
@@ -64,19 +65,24 @@ impl<'a> Token<'a> {
                     '(' => Exp(source, index, length + 1, depth + 1),
                     _ => Exp(source, index, length + 1, depth)
                 },
-            }
+            };
+            chars = next
         }
         Ok(("", state))
     }
 
-    pub fn number (digits: &str) -> usize {
+    pub const fn number (digits: &str) -> usize {
         let mut value = 0;
-        for c in digits.chars() { value = 10 * value + Self::digit(c); }
+        let mut chars = konst::string::char_indices(digits);
+        while let Some(((_, c), next)) = chars.next() {
+            value = 10 * value + Self::digit(c);
+            chars = next
+        }
         value
     }
 
     pub const fn digit (c: char) -> usize {
         match c { '0' => 0, '1' => 1, '2' => 2, '3' => 3, '4' => 4,
-                  '5' => 5, '6' => 6, '7' => 7, '8' => 8, '9' => 9, _ => unreachable!() }
+                  '5' => 5, '6' => 6, '7' => 7, '8' => 8, '9' => 9, _ => panic!("not a digit") }
     }
 }