rustfst 1.3.0

Library for constructing, combining, optimizing, and searching weighted finite-state transducers (FSTs).
Documentation 
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use std::cell::RefCell;

use anyhow::{Context, Result};

use crate::algorithms::encode::{EncodeTable, EncodeTableMut, EncodeType};
use crate::algorithms::{FinalTr, MapFinalAction, TrMapper};
use crate::fst_properties::FstProperties;
use crate::fst_traits::MutableFst;
use crate::{Label, Semiring, Tr};

struct EncodeMapper<W: Semiring> {
    encode_table: EncodeTable<W>,
}

impl<W: Semiring> EncodeMapper<W> {
    pub fn new(encode_type: EncodeType) -> Self {
        EncodeMapper {
            encode_table: EncodeTable(RefCell::new(EncodeTableMut::new(encode_type))),
        }
    }

    pub fn encode_weights(&self) -> bool {
        self.encode_table.0.borrow().encode_type.encode_weights()
    }

    pub fn encode_labels(&self) -> bool {
        self.encode_table.0.borrow().encode_type.encode_labels()
    }
}

impl<W: Semiring> TrMapper<W> for EncodeMapper<W> {
    fn tr_map(&self, tr: &mut Tr<W>) -> Result<()> {
        let tuple = self.encode_table.0.borrow().tr_to_tuple(tr);
        let label = self.encode_table.0.borrow_mut().encode(tuple) as Label;
        tr.ilabel = label;
        if self.encode_labels() {
            tr.olabel = label;
        }
        if self.encode_weights() {
            tr.weight.set_value(W::one().take_value());
        }
        Ok(())
    }

    fn final_tr_map(&self, final_tr: &mut FinalTr<W>) -> Result<()> {
        if self.encode_weights() {
            let tuple = self.encode_table.0.borrow().final_tr_to_tuple(final_tr);
            let label = self.encode_table.0.borrow_mut().encode(tuple) as Label;
            final_tr.ilabel = label;
            if self.encode_labels() {
                final_tr.olabel = label;
            }
            if self.encode_weights() {
                final_tr.weight.set_value(W::one().take_value());
            }
        }
        Ok(())
    }

    fn final_action(&self) -> MapFinalAction {
        if self.encode_weights() {
            MapFinalAction::MapRequireSuperfinal
        } else {
            MapFinalAction::MapNoSuperfinal
        }
    }

    fn properties(&self, inprops: FstProperties) -> FstProperties {
        let outprops = inprops;
        let mut mask = FstProperties::all_properties();
        if self.encode_labels() {
            mask &= FstProperties::i_label_invariant_properties()
                & FstProperties::o_label_invariant_properties();
        }
        if self.encode_weights() {
            mask &= FstProperties::i_label_invariant_properties()
                & FstProperties::weight_invariant_properties()
                & FstProperties::add_super_final_properties()
        }
        outprops & mask
    }
}

/// The `encode` operation allows the representation of a weighted transducer as a weighted automaton,
/// an unweighted transducer or an unweighted automaton by considering the pair
/// (input label, output), the pair (input label, weight) or the triple (input label,
/// output label, weight) as a single label depending on the value
/// of the encode flags: `encode_labels` and `encode_weights`.
///
/// The encoding of each pair or triple of labels and/or weights as a unique key is stored
/// in an `EncodeTable` object.
pub fn encode<W, F>(fst: &mut F, encode_type: EncodeType) -> Result<EncodeTable<W>>
where
    W: Semiring,
    F: MutableFst<W>,
{
    let mut encode_mapper = EncodeMapper::new(encode_type);
    fst.tr_map(&mut encode_mapper)
        .with_context(|| format_err!("Error calling TrMap with EncodeMapper."))?;
    Ok(encode_mapper.encode_table)
}