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1 files changed, 147 insertions, 0 deletions

diff --git a/base/src/bjc/dicelang/expr/Parser.java b/base/src/bjc/dicelang/expr/Parser.java
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+++ b/base/src/bjc/dicelang/expr/Parser.java
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+package bjc.dicelang.expr;
+
+import java.util.Arrays;
+import java.util.Scanner;
+
+import bjc.utils.data.ITree;
+import bjc.utils.funcdata.FunctionalList;
+import bjc.utils.parserutils.TreeConstructor;
+
+/**
+ * Parser for simple math expressions.
+ *
+ * @author Ben Culkin
+ */
+public class Parser {
+	/*
+	 * @TODO 10/08/17 Ben Culkin :MainSeperation
+	 * 	This main method should be moved to its own class.
+	 */
+	/**
+	 * Main method.
+	 *
+	 * @param args
+	 *                Unused CLI args.
+	 */
+	public static void main(final String[] args) {
+		/* Create our objects. */
+		final Tokens toks = new Tokens();
+		final Lexer lex = new Lexer();
+
+		/* Prepare our input source. */
+		final Scanner scan = new Scanner(System.in);
+
+		/* Read initial command. */
+		System.out.print("Enter a math expression (blank line to quit): ");
+		String ln = scan.nextLine().trim();
+
+		/* Enter REPL loop. */
+		while (!ln.equals("")) {
+			/* Print raw command. */
+			System.out.println("Raw command: " + ln);
+			System.out.println();
+
+			/* Lex command to infix tokens. */
+			final Token[] infixTokens = lex.lexString(ln, toks);
+			System.out.println("Lexed tokens: ");
+			for (final Token tok : infixTokens) {
+				System.out.println("\t" + tok);
+			}
+
+			/* Print out infix expression. */
+			System.out.print("Lexed expression: ");
+			for (final Token tok : infixTokens) {
+				System.out.print(tok.toExpr() + " ");
+			}
+
+			/* Space stages. */
+			System.out.println();
+			System.out.println();
+
+			/* Shunt infix tokens to postfix tokens. */
+			final Token[] postfixTokens = Shunter.shuntTokens(infixTokens);
+			System.out.println("Lexed tokens: ");
+			for (final Token tok : postfixTokens) {
+				System.out.println("\t" + tok);
+			}
+
+			/* Print out postfix tokens. */
+			System.out.print("Shunted expression: ");
+			for (final Token tok : postfixTokens) {
+				System.out.print(tok.toExpr() + " ");
+			}
+
+			/* Space stages. */
+			System.out.println();
+			System.out.println();
+
+			/* Construct a list from the array of tokens. */
+			final FunctionalList<Token> tokList = new FunctionalList<>(
+					Arrays.asList(postfixTokens));
+
+			/* Construct a tree from the list of postfixed tokens. */
+			final ITree<Token> ast = TreeConstructor.constructTree(tokList,
+					tok -> tok.typ.isOperator);
+
+			/* Print the tree, then the canonical expression for it. */
+			System.out.println("Parsed tree");
+			System.out.println(ast.toString());
+			System.out.println("\nCanonical expr: " + toCanonicalExpr(ast));
+
+			/* Space stages. */
+			System.out.println();
+			System.out.println();
+
+			/* Prompt for a new expression. */
+			System.out.print("Enter a math expression (blank line to quit): ");
+			/* Read it. */
+			ln = scan.nextLine().trim();
+		}
+
+		/* Cleanup after ourselves. */
+		scan.close();
+	}
+
+	/*
+	 * Convert an expression to one that uses the smallest necessary amount
+	 * of parens.
+	 */
+	private static String toCanonicalExpr(final ITree<Token> ast) {
+		final Token data = ast.getHead();
+
+		if (ast.getChildrenCount() == 0) {
+			/* Handle leaf nodes. */
+			return data.toExpr();
+		}
+
+		/* The left/right children. */
+		final ITree<Token> left  = ast.getChild(0);
+		final ITree<Token> right = ast.getChild(1);
+
+		/* Recursively canonicalize them. */
+		String leftExpr  = toCanonicalExpr(left);
+		String rightExpr = toCanonicalExpr(right);
+
+		/* Add parens if the left was higher priority. */
+		if (left.getChildrenCount() == 0) {
+			int leftPriority = left.getHead().typ.operatorPriority;
+			int dataPriority = data.typ.operatorPriority;
+
+			if (leftPriority >= dataPriority) {
+				leftExpr = String.format("(%s)", leftExpr);
+			}
+		}
+
+		/* Add parens if the right was higher priority. */
+		if (right.getChildrenCount() == 0) {
+			int rightPriority = right.getHead().typ.operatorPriority;
+			int dataPriority  = data.typ.operatorPriority;
+
+			if (rightPriority >= dataPriority) {
+				rightExpr = String.format("(%s)", rightExpr);
+			}
+		}
+
+		return String.format("%s %s %s", leftExpr, data.toExpr(), rightExpr);
+	}
+}