65 lines
1.8 KiB
Java
65 lines
1.8 KiB
Java
package de.plugh.compositeparse.parsers;
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import de.plugh.compositeparse.Block;
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import de.plugh.compositeparse.Pair;
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import de.plugh.compositeparse.ParseException;
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import de.plugh.compositeparse.Parser;
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import java.util.ArrayList;
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import java.util.Collections;
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import java.util.List;
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import java.util.function.Function;
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/**
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* Decide which parser to use from a list of "body" parsers and their "head"s.
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* <p>
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* If a "head" parses successfully, the corresponding "body" parser must be successful, otherwise a parse exception is
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* raised. If no "head" is successful, the {@link Decision} parser fails too.
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*
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* @param <T> return type of the parser
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*/
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public class Decision<T> implements Parser<T> {
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private final List<Pair<Parser<?>, Parser<T>>> pairs;
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/**
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* Create a new {@link Decision} parser from all passed arguments, which are "head"-"body" pairs.
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*
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* @param pairs multiple "head"-"body" pairs
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*/
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@SafeVarargs
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public Decision(Pair<Parser<?>, Parser<T>>... pairs) {
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this.pairs = new ArrayList<>();
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Collections.addAll(this.pairs, pairs);
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}
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/**
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* Create a new {@link Decision} parser from a list of "head"-"body" pairs.
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*
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* @param pairs a list of "head"-"body" pairs
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*/
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public Decision(List<Pair<Parser<?>, Parser<T>>> pairs) {
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this.pairs = new ArrayList<>(pairs);
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}
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@Override
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public Function<List<Block>, String> getNamingScheme() {
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return Block::alternative;
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}
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@Override
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public T read(Block block) throws ParseException {
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for (Pair<Parser<?>, Parser<T>> pair : pairs) {
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try {
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pair.getFirst().parse(block);
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} catch (ParseException e) {
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continue;
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}
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return pair.getSecond().parse(block);
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}
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throw new ParseException(block);
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}
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}
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