cfg-predict-sets 0.1.1

Library for manipulating context-free grammars.
Documentation 
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//! LAST sets.

use cfg_grammar::Cfg;

use crate::PerSymbolSets;
use crate::PredictSets;
use crate::cfg_sets_ext::CfgSetsExt;

/// FIRST sets.
pub struct LastSets {
    map: PerSymbolSets,
}

impl LastSets {
    /// Compute all LAST sets of the grammar.
    ///
    /// We define a binary relation LAST(N, S), in which N is related to S
    /// if the grammar has a production of the form `N ⸬= α S β`, where
    /// β is a nullable string of symbols.
    ///
    /// We return the transitive closure of this relation.
    pub fn new(grammar: &Cfg) -> Self {
        let mut reversed_grammar = grammar.clone();
        reversed_grammar.reverse();
        let map = {
            let first_sets = reversed_grammar.first_sets();
            // E0597: `reversed_grammar` does not live long enough
            //   label: borrowed value does not live long enough
            first_sets.map
        };
        LastSets { map }
    }
}

impl PredictSets for LastSets {
    /// Returns a reference to LAST sets.
    fn predict_sets(&self) -> &PerSymbolSets {
        &self.map
    }
}