Implement basic parser

src/parser.rs

@@ -0,0 +1,39 @@
+use crate::lexer::Token;
+use crate::lexer::Tokens;
+
+
+#[derive(Debug)]
+pub enum Datum {
+    Boolean(bool),
+    Number(i64),
+    Symbol(String),
+    List(Vec<Datum>),
+}
+
+pub fn parse(tokens: Tokens) -> Datum {
+    let (datum, _) = parse_datum(&tokens, 0);
+    datum
+}
+
+fn parse_datum(tokens: &Tokens, ix: usize) -> (Datum, usize) {
+    match &tokens[ix] {
+        Token::Identifier(s) => (Datum::Symbol(s.to_string()), ix + 1),
+        Token::Boolean(b) => (Datum::Boolean(*b), ix + 1),
+        Token::Number(n) => (Datum::Number(*n), ix + 1),
+        Token::LeftRoundBracket => parse_list(tokens, ix + 1),
+        _ => panic!("Unexpected token {:?}", tokens[ix])
+    }
+}
+
+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 {
+        let (datum, new_ix) = parse_datum(tokens, ix);
+        datums.push(datum);
+        ix = new_ix;
+    }
+
+    (Datum::List(datums), ix + 1)
+}