mathjs/lib/expression/node/ConditionalNode.js

var Node = require('./Node');
var latex = require('../../util/latex');

/**
 * A lazy evaluating conditional operator: 'condition ? trueExpr : falseExpr'
 *
 * @param {Node} condition   Condition, must result in a boolean
 * @param {Node} trueExpr    Expression evaluated when condition is true
 * @param {Node} falseExpr   Expression evaluated when condition is true
 *
 * @constructor ConditionalNode
 * @extends {Node}
 */
function ConditionalNode (condition, trueExpr, falseExpr) {
  if (!(this instanceof ConditionalNode)) {
    throw new SyntaxError('Constructor must be called with the new operator');
  }
  if (!(condition instanceof Node)) throw new TypeError('Parameter condition must be a Node');
  if (!(trueExpr instanceof Node))  throw new TypeError('Parameter trueExpr must be a Node');
  if (!(falseExpr instanceof Node)) throw new TypeError('Parameter falseExpr must be a Node');

  this.condition = condition;
  this.trueExpr = trueExpr;
  this.falseExpr = falseExpr;
}

ConditionalNode.prototype = new Node();

ConditionalNode.prototype.type = 'ConditionalNode';

/**
 * Compile the node to javascript code
 * @param {Object} defs     Object which can be used to define functions
 *                          or constants globally available for the compiled
 *                          expression
 * @return {String} js
 * @private
 */
ConditionalNode.prototype._compile = function(defs) {
  // TODO: it would be faster instead of executing math.ifElse, to inline ifElse
  return (
      'math.ifElse(' + this.condition._compile(defs) + ', true, false) ? ' +
      '( ' + this.trueExpr._compile(defs) + ') : ' +
      '( ' + this.falseExpr._compile(defs) + ')'
      );
};

/**
 * Find all nodes matching given filter
 * @param {Object} filter  See Node.find for a description of the filter options
 * @returns {Node[]} nodes
 */
ConditionalNode.prototype.find = function (filter) {
  var nodes = [];

  // check itself
  if (this.match(filter)) {
    nodes.push(this);
  }

  // search in parameters
  nodes = nodes.concat(
      this.condition.find(filter),
      this.trueExpr.find(filter),
      this.falseExpr.find(filter));

  return nodes;
};

/**
 * Get string representation
 * @return {String} str
 */
ConditionalNode.prototype.toString = function() {
  // TODO: not nice adding parenthesis al the time
  return '(' + this.condition.toString() + ') ? (' +
      this.trueExpr.toString() + ') : (' +
      this.falseExpr.toString() + ')';
};

/**
 * Get LaTeX representation
 * @return {String} str
 */
ConditionalNode.prototype.toTex = function() {
  var s = (
      latex.addBraces(this.trueExpr.toTex()) +
      ', &\\quad' +
      latex.addBraces('\\text{if}\\;' + this.condition.toTex())
      ) + '\\\\' + (
      latex.addBraces(this.falseExpr.toTex()) +
      ', &\\quad' +
      latex.addBraces('\\text{otherwise}')
      );

  return latex.addBraces(s, [
    '\\left\\{\\begin{array}{l l}',
    '\\end{array}\\right.'
  ]);
};

module.exports = ConditionalNode;