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package bjc.dicelang.expr;
import bjc.utils.data.ITree;
import bjc.utils.funcdata.FunctionalList;
import bjc.utils.parserutils.TreeConstructor;
import java.util.Arrays;
import java.util.Scanner;
/**
* Parser for simple math expressions.
*
* @author Ben Culkin
*/
public class Parser {
/**
* Main method.
*
* @param args
* Unused CLI args.
*/
public static void main(String[] args) {
/*
* Create our objects.
*/
Tokens toks = new Tokens();
Lexer lex = new Lexer();
/*
* Prepare our input.
*/
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.
*/
Token[] infixTokens = lex.lexString(ln, toks);
System.out.println("Lexed tokens: ");
for(Token tok : infixTokens) {
System.out.println("\t" + tok);
}
/*
* Print out infix expression.
*/
System.out.print("Lexed expression: ");
for(Token tok : infixTokens) {
System.out.print(tok.toExpr() + " ");
}
System.out.println();
System.out.println();
/*
* Shunt infix tokens to postfix tokens.
*/
Token[] postfixTokens = Shunter.shuntTokens(infixTokens);
System.out.println("Lexed tokens: ");
for(Token tok : postfixTokens) {
System.out.println("\t" + tok);
}
/*
* Print out postfix tokens.
*/
System.out.print("Shunted expression: ");
for(Token tok : postfixTokens) {
System.out.print(tok.toExpr() + " ");
}
System.out.println();
System.out.println();
FunctionalList<Token> tokList = new FunctionalList<>(Arrays.asList(postfixTokens));
ITree<Token> ast = TreeConstructor.constructTree(tokList, tok -> tok.type.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));
System.out.println();
/*
* Prompt for a new expression.
*/
System.out.print("Enter a math expression (blank line to quit): ");
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(ITree<Token> ast) {
Token data = ast.getHead();
if(ast.getChildrenCount() == 0)
/*
* Handle leaf nodes.
*/
return data.toExpr();
else {
ITree<Token> left = ast.getChild(0);
ITree<Token> right = ast.getChild(1);
String leftExpr = toCanonicalExpr(left);
String rightExpr = toCanonicalExpr(right);
/*
* Add parens if the left was higher priority.
*/
if(left.getChildrenCount() == 0) {
if(left.getHead().type.operatorPriority >= data.type.operatorPriority) {
leftExpr = "(" + leftExpr + ")";
}
}
/*
* Add parens if the right was higher priority.
*/
if(right.getChildrenCount() == 0) {
if(right.getHead().type.operatorPriority >= data.type.operatorPriority) {
rightExpr = "(" + rightExpr + ")";
}
}
return leftExpr + " " + data.toExpr() + " " + rightExpr;
}
}
}
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