Add numeric maths filter operators

There are other ways we could add maths to TW5 (including @EvanBalster's awesome https://github.com/EvanBalster/TiddlyWikiFormula) but the approach here has the merit of simplicity because it reuses the existing filter evaluation mechanism. That means that it's not ordinary "2+2" maths, it's a unique list processing language...

Docs to come

Fixes #254

core/modules/filters/math.js

@@ -0,0 +1,130 @@
+/*\
+title: $:/core/modules/filters/math.js
+type: application/javascript
+module-type: filteroperator
+
+Filter operators for math. Unary/binary operators work on each item in turn, and return a new item list.
+
+Sum/product/maxall/minall operate on the entire list, returning a single item.
+
+Note that strings are converted to numbers automatically. Trailing non-digits are ignored.
+
+* "" converts to 0
+* "12kk" converts to 12
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+exports.negate = makeNumericBinaryOperator(
+	function(a) {return -a}
+);
+
+exports.abs = makeNumericBinaryOperator(
+	function(a) {return Math.abs(a)}
+);
+
+exports.ceil = makeNumericBinaryOperator(
+	function(a) {return Math.ceil(a)}
+);
+
+exports.floor = makeNumericBinaryOperator(
+	function(a) {return Math.floor(a)}
+);
+
+exports.round = makeNumericBinaryOperator(
+	function(a) {return Math.round(a)}
+);
+
+exports.trunc = makeNumericBinaryOperator(
+	function(a) {return Math.trunc(a)}
+);
+
+exports.sign = makeNumericBinaryOperator(
+	function(a) {return Math.sign(a)}
+);
+
+exports.add = makeNumericBinaryOperator(
+	function(a,b) {return a + b;}
+);
+
+exports.subtract = makeNumericBinaryOperator(
+	function(a,b) {return a - b;}
+);
+
+exports.multiply = makeNumericBinaryOperator(
+	function(a,b) {return a * b;}
+);
+
+exports.divide = makeNumericBinaryOperator(
+	function(a,b) {return a / b;}
+);
+
+exports.remainder = makeNumericBinaryOperator(
+	function(a,b) {return a % b;}
+);
+
+exports.max = makeNumericBinaryOperator(
+	function(a,b) {return Math.max(a,b);}
+);
+
+exports.min = makeNumericBinaryOperator(
+	function(a,b) {return Math.min(a,b);}
+);
+
+exports.sum = makeNumericArrayOperator(
+	function(accumulator,value) {return accumulator + value},
+	0 // Initial value
+);
+
+exports.product = makeNumericArrayOperator(
+	function(accumulator,value) {return accumulator * value},
+	1 // Initial value
+);
+
+exports.maxall = makeNumericArrayOperator(
+	function(accumulator,value) {return Math.max(accumulator,value)},
+	-Infinity // Initial value
+);
+
+exports.minall = makeNumericArrayOperator(
+	function(accumulator,value) {return Math.min(accumulator,value)},
+	Infinity // Initial value
+);
+
+function makeNumericBinaryOperator(fnCalc) {
+	return function(source,operator,options) {
+		var result = [],
+			numOperand = parseNumber(operator.operand);
+		source(function(tiddler,title) {
+			result.push(stringifyNumber(fnCalc(parseNumber(title),numOperand)));
+		});
+		return result;
+	};
+};
+
+function makeNumericArrayOperator(fnCalc,initialValue) {
+	initialValue = initialValue || 0;
+	return function(source,operator,options) {
+		var result = [];
+		source(function(tiddler,title) {
+			result.push(title);
+		});
+		return [stringifyNumber(result.reduce(function(accumulator,currentValue) {
+			return fnCalc(accumulator,parseNumber(currentValue));
+		},initialValue))];
+	};
+};
+
+function parseNumber(str) {
+	return parseFloat(str) || 0;
+}
+
+function stringifyNumber(num) {
+	return num + "";
+}
+
+})();

editions/test/tiddlers/tests/test-filters.js

@@ -361,6 +361,20 @@ describe("Filter tests", function() {
 		expect(wiki.filterTiddlers("[list[TiddlerSeventh]before[MissingTiddler]]").join(",")).toBe("a fourth tiddler");
 	});
 
+	it("should handle the math operators", function() {
+		expect(wiki.filterTiddlers("[[2]add[2]]").join(",")).toBe("4");
+		expect(wiki.filterTiddlers("[[4]subtract[2]]").join(",")).toBe("2");
+		expect(wiki.filterTiddlers("[[24]divide[8]]").join(",")).toBe("3");
+		expect(wiki.filterTiddlers("[[355]divide[113]sign[]multiply[4]]").join(",")).toBe("4");
+		expect(wiki.filterTiddlers("[[355]divide[113]add[0.5]round[]multiply[4]]").join(",")).toBe("16");
+		expect(wiki.filterTiddlers("1 2 3 4 +[sum[]]").join(",")).toBe("10");
+		expect(wiki.filterTiddlers("1 2 3 4 +[product[]]").join(",")).toBe("24");
+		expect(wiki.filterTiddlers("1 2 3 4 +[maxall[]]").join(",")).toBe("4");
+		expect(wiki.filterTiddlers("1 2 3 4 +[minall[]]").join(",")).toBe("1");
+		expect(wiki.filterTiddlers("1 2 3 4 +[max[2]]").join(",")).toBe("2,2,3,4");
+		expect(wiki.filterTiddlers("1 2 3 4 +[min[2]]").join(",")).toBe("1,2,2,2");
+	});
+
 });
 
 })();