implement ast compactor v1

2020-12-11 17:38:23 +01:00
parent 1c62dbdfa5
commit ca9ce5dd45
1 changed files with 139 additions and 0 deletions
--- a/src/main/java/parser/ASTCompacter.java
+++ b/src/main/java/parser/ASTCompacter.java
@ -0,0 +1,139 @@
+package parser;
+
+import parser.grammar.Grammar;
+import util.ast.AST;
+import util.ast.Node;
+
+import java.util.Collection;
+import java.util.HashSet;
+
+import static util.tools.Logger.log;
+
+public final class ASTCompacter {
+
+    private ASTCompacter() {}
+
+    public static void clean(AST tree, Grammar grammar) {
+        int removed = 0;
+
+        int change;
+        do {
+            change = compact(tree, grammar)
+                     + removeEpsilon(tree, grammar)
+                     + removeNullable(tree, grammar);
+
+            removed += change;
+        } while (change != 0);
+
+        log(tree.toString());
+        log("\nCleaned Tree: " + removed + " nodes removed.");
+        log("-".repeat(100));
+    }
+
+    public static int compact(AST tree, Grammar grammar) {
+        int compacted = 0;
+
+        int changed;
+        do {
+            changed = compact(tree.getRoot(), grammar);
+            compacted += changed;
+        } while (changed != 0);
+
+        if (compacted != 0) {
+            log("Flattened " + compacted + " nodes.");
+            log("-".repeat(100));
+        }
+
+        return compacted;
+    }
+
+    private static int compact(Node root, Grammar grammar) {
+        int compacted = 0;
+        Collection<Node> toRemove = new HashSet<>();
+
+        for (Node child : root.getChildren()) {
+            if (grammar.hasCompact(root.getName())
+                && root.getChildren().size() == 1) {
+
+                log("Compacting " + root.getName() + " -> " + child.getName());
+
+                root.setName(child.getName());
+                root.setValue(child.getValue());
+                root.setChildren(child.getChildren());
+
+                toRemove.add(child);
+
+            } else {
+                compacted += compact(child, grammar);
+            }
+        }
+
+        root.getChildren().removeAll(toRemove);
+
+        return compacted + toRemove.size();
+    }
+
+    public static int removeNullable(AST tree, Grammar grammar) {
+        int removed = removeNullable(tree.getRoot(), grammar);
+
+        if (removed != 0) {
+            log("Removed " + removed + " nodes.");
+            log("-".repeat(100));
+        }
+
+        return removed;
+    }
+
+    private static int removeNullable(Node root, Grammar grammar) {
+        int removed = 0;
+        Collection<Node> toRemove = new HashSet<>();
+
+        for (Node child : root.getChildren()) {
+            if (grammar.hasNullable(child.getName())
+                && child.getValue().isEmpty()
+                && !child.hasChildren()) {
+
+                log("Removing " + child.getName());
+
+                toRemove.add(child);
+            } else {
+                removed += removeNullable(child, grammar);
+            }
+        }
+
+        root.getChildren().removeAll(toRemove);
+
+        return removed + toRemove.size();
+    }
+
+    // Returns the number of removed nodes
+    public static int removeEpsilon(AST tree, Grammar grammar) {
+        int removed = removeEpsilon(tree.getRoot(), grammar);
+
+        if (removed != 0) {
+            log("Removed " + removed + " nodes.");
+            log("-".repeat(100));
+        }
+
+        return removed;
+    }
+
+    private static int removeEpsilon(Node root, Grammar grammar) {
+        int removed = 0;
+        Collection<Node> toRemove = new HashSet<>();
+
+        for (Node child : root.getChildren()) {
+            if (child.getName().equals(grammar.getEpsilonSymbol()) && !child.hasChildren()) {
+                log("Removing " + root.getName() + " -> " + child.getName());
+                toRemove.add(child);
+            } else {
+                removed += removeEpsilon(child, grammar);
+            }
+        }
+
+        root.getChildren().removeAll(toRemove);
+
+        return removed + toRemove.size();
+    }
+
+}