Lex special symbols as one token

kalk/src/lexer.rs

@@ -116,6 +116,13 @@ impl<'a> Lexer<'a> {
             ';' => build(TokenKind::Semicolon, "", span),
             '%' => build(TokenKind::Percent, "", span),
             '\'' => build(TokenKind::Tick, "", span),
+            // Some of the special symbols will be lexed here,
+            // so that they don't merge with other symbols.
+            'π' => build(TokenKind::Identifier, "π", span),
+            '√' => build(TokenKind::Identifier, "√", span),
+            'τ' => build(TokenKind::Identifier, "τ", span),
+            'ϕ' => build(TokenKind::Identifier, "ϕ", span),
+            'Γ' => build(TokenKind::Identifier, "Γ", span),
             _ => build(TokenKind::Unknown, "", span),
         };
 
@@ -221,7 +228,7 @@ fn is_valid_identifier(c: Option<&char>) -> bool {
     if let Some(c) = c {
         match c {
             '+' | '-' | '/' | '*' | '%' | '^' | '!' | '(' | ')' | '=' | '.' | ',' | ';' | '|'
-            | '⌊' | '⌋' | '⌈' | '⌉' | ']' => false,
+            | '⌊' | '⌋' | '⌈' | '⌉' | ']' | 'π' | '√' | 'τ' | 'ϕ' | 'Γ' => false,
             _ => !c.is_digit(10),
         }
     } else {

kalk/src/parser.rs

@@ -481,10 +481,14 @@ fn parse_identifier(context: &mut Context) -> Result<Expr, CalcError> {
     let identifier = Identifier::from_full_name(&advance(context).value);
 
     // Eg. sqrt64
-    if match_token(context, TokenKind::Literal) {
+    if match_token(context, TokenKind::Literal)
+        || peek(context).value == "π"
+        || peek(context).value == "τ"
+        || peek(context).value == "ϕ"
+    {
         // If there is a function with this name, parse it as a function, with the next token as the argument.
         if context.symbol_table.contains_fn(&identifier.pure_name) {
-            let parameter = Expr::Literal(string_to_num(&advance(context).value));
+            let parameter = parse_primary(context)?;
             return Ok(Expr::FnCall(identifier, vec![parameter]));
         }
     }