cfg_predict/
last.rs

1//! FIRST sets.
2
3use cfg_grammar::RuleContainer;
4
5use super::FirstSets;
6use super::PerSymbolSets;
7use super::PredictSets;
8
9/// FIRST sets.
10pub struct LastSets {
11    map: PerSymbolSets,
12}
13
14impl LastSets {
15    /// Compute all LAST sets of the grammar.
16    ///
17    /// We define a binary relation LAST(N, S), in which N is related to S
18    /// if the grammar has a production of the form `N ⸬= α S β`, where
19    /// β is a nullable string of symbols.
20    ///
21    /// We compute the transitive closure of this relation.
22    pub fn new<G>(grammar: &G) -> Self
23    where
24        G: RuleContainer + Default,
25    {
26        let reversed_grammar = grammar.reverse();
27        let map = {
28            let first_sets = FirstSets::new(&reversed_grammar);
29            // E0597: `reversed_grammar` does not live long enough
30            //   label: borrowed value does not live long enough
31            first_sets.map
32        };
33        LastSets { map }
34    }
35}
36
37impl PredictSets for LastSets {
38    /// Returns a reference to FIRST sets.
39    fn predict_sets(&self) -> &PerSymbolSets {
40        &self.map
41    }
42}
cfg_predict/last.rs

cfg_predict/
last.rs
