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package bjc.dicelang.expr;
import bjc.data.ITree;
/**
* Parser for simple math expressions.
*
* @author Ben Culkin
*/
public class Parser {
/**
* Convert an expression to one that uses the smallest necessary amount of
* parens.
*
* @param ast
* The AST to canonicalize.
* @return The canonicalized AST.
*/
public 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);
}
}
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