163 lines
4.2 KiB
Java
163 lines
4.2 KiB
Java
package parser;
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import parser.grammar.Grammar;
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import util.ast.AST;
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import util.ast.Node;
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import java.util.Collection;
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import java.util.HashSet;
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import static util.tools.Logger.log;
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public final class ASTCompacter {
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private ASTCompacter() {}
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public static void clean(AST tree, Grammar grammar) {
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int removed = 0;
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int change;
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do {
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change = compact(tree, grammar)
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+ removeEpsilon(tree, grammar)
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+ removeNullable(tree, grammar);
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removed += change;
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} while (change != 0);
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rename(tree);
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log(tree.toString());
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log("\nCleaned Tree: " + removed + " nodes removed.");
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log("-".repeat(100));
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}
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public static int compact(AST tree, Grammar grammar) {
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int compacted = 0;
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int changed;
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do {
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changed = compact(tree.getRoot(), grammar);
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compacted += changed;
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} while (changed != 0);
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if (compacted != 0) {
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log("Flattened " + compacted + " nodes.");
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log("-".repeat(100));
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}
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return compacted;
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}
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private static int compact(Node root, Grammar grammar) {
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int compacted = 0;
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Collection<Node> toRemove = new HashSet<>();
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for (Node child : root.getChildren()) {
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if (grammar.hasCompact(root.getName())
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&& root.getChildren().size() == 1) {
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log("Compacting " + root.getName() + " -> " + child.getName());
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root.setName(child.getName());
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root.setValue(child.getValue());
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root.setChildren(child.getChildren());
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toRemove.add(child);
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} else {
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compacted += compact(child, grammar);
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}
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}
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root.getChildren().removeAll(toRemove);
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return compacted + toRemove.size();
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}
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public static int removeNullable(AST tree, Grammar grammar) {
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int removed = removeNullable(tree.getRoot(), grammar);
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if (removed != 0) {
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log("Removed " + removed + " nodes.");
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log("-".repeat(100));
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}
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return removed;
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}
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private static int removeNullable(Node root, Grammar grammar) {
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int removed = 0;
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Collection<Node> toRemove = new HashSet<>();
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for (Node child : root.getChildren()) {
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if (grammar.hasNullable(child.getName())
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&& child.getValue().isEmpty()
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&& !child.hasChildren()) {
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log("Removing " + child.getName());
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toRemove.add(child);
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} else {
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removed += removeNullable(child, grammar);
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}
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}
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root.getChildren().removeAll(toRemove);
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return removed + toRemove.size();
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}
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// Returns the number of removed nodes
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public static int removeEpsilon(AST tree, Grammar grammar) {
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int removed = removeEpsilon(tree.getRoot(), grammar);
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if (removed != 0) {
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log("Removed " + removed + " nodes.");
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log("-".repeat(100));
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}
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return removed;
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}
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private static int removeEpsilon(Node root, Grammar grammar) {
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int removed = 0;
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Collection<Node> toRemove = new HashSet<>();
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for (Node child : root.getChildren()) {
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if (child.getName().equals(grammar.getEpsilonSymbol()) && !child.hasChildren()) {
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log("Removing " + root.getName() + " -> " + child.getName());
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toRemove.add(child);
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} else {
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removed += removeEpsilon(child, grammar);
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}
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}
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root.getChildren().removeAll(toRemove);
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return removed + toRemove.size();
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}
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private static void rename(AST tree) {
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rename(tree.getRoot());
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log("-".repeat(100));
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}
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private static void rename(Node root) {
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String newName = switch (root.getName()) {
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case "EXPR_2", "EXPR_F" -> "EXPR";
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default -> root.getName();
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};
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if (!newName.equals(root.getName())) {
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log("Rename " + root.getName() + " to " + newName + ".");
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}
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root.setName(newName);
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for (Node child : root.getChildren()) {
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rename(child);
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}
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}
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}
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