initial ideas

lang2/peg.js

@@ -0,0 +1,28 @@
+const Expression = rule(
+	[{head: Term}, {tail: star([_, slash("+", "-"), _, Term])}],
+	({head, tail}) => {
+		return tail.reduce(function(result, element) {
+			if (element[1] === "+") { return result + element[3]; }
+			if (element[1] === "-") { return result - element[3]; }
+		}, head);
+	}
+);
+
+const Term = rule(
+	[{head: Factor}, {tail: star([_, slash("*", "/"), _, Factor])}],
+	({head, tail}) => {
+		return tail.reduce(function(result, element) {
+			if (element[1] === "*") { return result * element[3]; }
+			if (element[1] === "/") { return result / element[3]; }
+		}, head);
+	}
+);
+
+const Factor = slash(
+	rule(["(", _, {expr: Expression}, _, ")"], ({expr}) => expr),
+	Integer
+);
+
+const Integer = rule([_, /[0-9]+/], () => { return parseInt(text(), 10); });
+
+const _ = /[ \t\n\r]*/;