Add probability weighting

README.md

@@ -7,7 +7,7 @@ Purrchance is an unofficial Rust implementation of the
 
 - [ ] Parsing grammars from text format
 - [x] Basic lists
-- [ ] Probability weights
+- [x] Probability weights
 - [ ] Single-item lists
 - [ ] Escape sequences
 - [ ] Shorthand lists

src/lib.rs

@@ -29,11 +29,11 @@ impl Purrchance for Expr {
     }
 }
 
-pub struct List(Vec<Expr>);
+pub struct List(Vec<(Expr, f64)>);
 
 impl Purrchance for List {
     fn eval(&self, g: &Grammar) -> Option<String> {
-        self.0.choose(&mut thread_rng())?.eval(g)
+        self.0.choose_weighted(&mut thread_rng(), |item| item.1).ok()?.0.eval(g)
     }
 }
 
@@ -64,7 +64,7 @@ mod tests {
         let sym1 = Symbol::Terminal("hell".to_string());
         let sym2 = Symbol::Terminal("o world".to_string());
         let expr = Expr(vec![sym1, sym2]);
-        let list = List(vec![expr]);
+        let list = List(vec![(expr, 1.0)]);
         let g = Grammar(HashMap::new());
         assert_eq!(list.eval(&g), Some("hello world".to_string()));
     }
@@ -73,7 +73,7 @@ mod tests {
     fn eval_multiple_terminals_expr_list() {
         let sym1 = Symbol::Terminal("hello".to_string());
         let sym2 = Symbol::Terminal("goodbye".to_string());
-        let list = List(vec![Expr(vec![sym1]), Expr(vec![sym2])]);
+        let list = List(vec![(Expr(vec![sym1]), 1.0), (Expr(vec![sym2]), 1.0)]);
         let g = Grammar(HashMap::new());
         assert!(vec![Some("hello".to_string()), Some("goodbye".to_string())].contains(&list.eval(&g)));
     }
@@ -88,7 +88,7 @@ mod tests {
     #[test]
     fn eval_valid_nonterminal() {
         let term = Symbol::Terminal("hello world".to_string());
-        let list = List(vec![Expr(vec![term])]);
+        let list = List(vec![(Expr(vec![term]), 1.0)]);
         let mut g = Grammar(HashMap::new());
         g.0.insert("output".to_string(), list);
         let nt = Symbol::NonTerminal("output".to_string());
@@ -98,7 +98,7 @@ mod tests {
     #[test]
     fn eval_missing_nonterminal() {
         let term = Symbol::Terminal("hello world".to_string());
-        let list = List(vec![Expr(vec![term])]);
+        let list = List(vec![(Expr(vec![term]), 1.0)]);
         let mut g = Grammar(HashMap::new());
         g.0.insert("output".to_string(), list);
         let nt = Symbol::NonTerminal("missing".to_string());