Initial version of environment model

src/parser.rs

@@ -1,7 +1,7 @@
 use crate::lexer::Token;
 use crate::lexer::Tokens;
 
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub enum Datum {
     Boolean(bool),
     Number(i64),
@@ -11,6 +11,10 @@ pub enum Datum {
     Unspecified,
 }
 
+pub fn make_symbol(s: &str) -> Datum {
+    Datum::Symbol(s.to_string())
+}
+
 impl Default for Datum {
     fn default() -> Self {
         Datum::Unspecified
@@ -35,12 +39,14 @@ fn parse_datum(tokens: &Tokens, ix: usize) -> (Datum, usize) {
 pub fn parse_list(tokens: &Tokens, mut ix: usize) -> (Datum, usize) {
     let mut datums = vec![];
 
-    // FIXME: will crash when RightRoundBracket is missing
-    while tokens[ix] != Token::RightRoundBracket {
+    while ix < tokens.len() && tokens[ix] != Token::RightRoundBracket {
         let (datum, new_ix) = parse_datum(tokens, ix);
         datums.push(datum);
         ix = new_ix;
     }
+    if ix == tokens.len() {
+        panic!("PARSE_LIST -- missing closing bracket {:?}", tokens)
+    }
 
     (Datum::List(datums), ix + 1)
 }