From a8681ca6d13586cc2c07f0ab93f4804c77255ac4 Mon Sep 17 00:00:00 2001
From: bculkin2442 <bjculkin@mix.wvu.edu>
Date: Fri, 18 Mar 2016 15:13:06 -0400
Subject: Added a thing to build ASTs from shunted (postfix) expressions

---
 .../bjc/utils/parserutils/TreeConstructor.java     | 66 ++++++++++++++++++++++
 1 file changed, 66 insertions(+)
 create mode 100644 BJC-Utils2/src/main/java/bjc/utils/parserutils/TreeConstructor.java

(limited to 'BJC-Utils2/src/main/java/bjc/utils/parserutils')

diff --git a/BJC-Utils2/src/main/java/bjc/utils/parserutils/TreeConstructor.java b/BJC-Utils2/src/main/java/bjc/utils/parserutils/TreeConstructor.java
new file mode 100644
index 0000000..9c920d2
--- /dev/null
+++ b/BJC-Utils2/src/main/java/bjc/utils/parserutils/TreeConstructor.java
@@ -0,0 +1,66 @@
+package bjc.utils.parserutils;
+
+import java.util.Deque;
+import java.util.LinkedList;
+import java.util.function.Predicate;
+
+import bjc.utils.data.GenHolder;
+import bjc.utils.data.Pair;
+import bjc.utils.funcdata.FunctionalList;
+
+/**
+ * Creates a parse tree from a postfix expression
+ * 
+ * @author ben
+ *
+ * @param <T>
+ *            The elements of the parse tree
+ */
+public class TreeConstructor {
+	/**
+	 * Construct a tree from a list of tokens in postfix notation
+	 * 
+	 * Only binary operators are accepted.
+	 * 
+	 * @param toks
+	 *            The list of tokens to build a tree from
+	 * @param opPredicate
+	 *            The predicate to use to determine if something is a
+	 *            operator
+	 * @return A AST from the expression
+	 */
+	public static <T> AST<T> constructTree(FunctionalList<T> toks,
+			Predicate<T> opPredicate) {
+		GenHolder<Pair<Deque<AST<T>>, AST<T>>> initState = new GenHolder<>(
+				new Pair<>(new LinkedList<>(), null));
+
+		toks.forEach((ele) -> {
+			if (opPredicate.test(ele)) {
+				initState.transform((par) -> {
+					Deque<AST<T>> lft = par.merge((deq, ast) -> deq);
+
+					AST<T> mergedAST = par.merge((deq, ast) -> {
+						AST<T> right = deq.pop();
+						AST<T> left = deq.pop();
+
+						AST<T> newAST = new AST<T>(ele, left, right);
+
+						deq.push(newAST);
+						
+						return newAST;
+					});
+
+					Pair<Deque<AST<T>>, AST<T>> newPair = new Pair<>(lft,
+							mergedAST);
+
+					return newPair;
+				});
+			} else {
+				initState.doWith((par) -> par
+						.doWith((deq, ast) -> deq.push(new AST<>(ele))));
+			}
+		});
+
+		return initState.unwrap((par) -> par.merge((deq, ast) -> ast));
+	}
+}
-- 
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