[lexer] Clean up named_char module

lexer/src/named_char.rs

@@ -2,8 +2,8 @@
  * Eryn Wells <eryn@erynwells.me>
  */
 
-use std::collections::HashSet;
-use sibiltypes::Char;
+use std::collections::HashMap;
+use std::sync::{Once, ONCE_INIT};
 
 const ALARM: &'static str = "alarm";
 const BACKSPACE: &'static str = "backspace";
@@ -15,31 +15,46 @@ const RETURN: &'static str = "return";
 const SPACE: &'static str = "space";
 const TAB: &'static str = "tab";
 
-pub fn set() -> HashSet<&'static str> {
-    let mut set: HashSet<&'static str> = HashSet::new();
-    set.insert(ALARM);
-    set.insert(BACKSPACE);
-    set.insert(DELETE);
-    set.insert(ESCAPE);
-    set.insert(NEWLINE);
-    set.insert(NULL);
-    set.insert(RETURN);
-    set.insert(SPACE);
-    set.insert(TAB);
-    set
+/// Mapping of names to `char` values. Returns the name of the given character, if a name exists.
+/// Otherwise, returns `None`.
+fn char_for(named: &str) -> Option<char> {
+    static ONCE = ONCE_INIT;
+    static mut names_to_chars: HashMap<&'static str, char>;
+    unsafe {
+        ONCE.call_once(|| {
+            names_to_chars = HashMap::new();
+            names_to_chars.insert(ALARM, '\x07');
+            names_to_chars.insert(BACKSPACE, '\x08');
+            names_to_chars.insert(DELETE, '\x7F');
+            names_to_chars.insert(ESCAPE, '\x1B');
+            names_to_chars.insert(NEWLINE, '\n');
+            names_to_chars.insert(NULL, '\0');
+            names_to_chars.insert(RETURN, '\r');
+            names_to_chars.insert(SPACE, ' ');
+            names_to_chars.insert(TAB, '\t');
+        });
+        names_to_chars.get(named)
+    }
 }
 
-pub fn char_named_by(named: &str) -> Char {
-    Char(match named {
-        ALARM => '\x07',
-        BACKSPACE => '\x08',
-        DELETE => '\x7F',
-        ESCAPE => '\x1B',
-        NEWLINE => '\n',
-        NULL => '\0',
-        RETURN => '\r',
-        SPACE => ' ',
-        TAB => '\t',
-        _ => panic!("char_named_by called with invalid named char string")
-    })
+/// Mapping of `char` values to names. Returns the name of the given character, if a name exists.
+/// Otherwise, returns `None`.
+fn name_of(c: char) -> Option<&'static str> {
+    static ONCE = ONCE_INIT;
+    static mut chars_to_names: HashMap<char, &'static str>;
+    unsafe {
+        ONCE.call_once(|| {
+            chars_to_names = HashMap::new();
+            chars_to_names.insert('\x07', ALARM);
+            chars_to_names.insert('\x08', BACKSPACE);
+            chars_to_names.insert('\x7F', DELETE);
+            chars_to_names.insert('\x1B', ESCAPE);
+            chars_to_names.insert('\n', NEWLINE);
+            chars_to_names.insert('\0', NULL);
+            chars_to_names.insert('\r', RETURN);
+            chars_to_names.insert(' ', SPACE);
+            chars_to_names.insert('\t', TAB);
+        });
+        chars_to_names.get(c)
+    }
 }