fix existing tags

new tags: for,cycle

expression.js

@@ -0,0 +1,54 @@
+const syntax = require('./syntax.js');
+const Exp = require('./expression.js');
+const lexical = require('./lexical.js');
+const _ = require('lodash');
+
+function evalExp(exp, scope) {
+    if (!scope) throw new Error('unable to evalExp: scope undefined');
+    var operatorREs = lexical.operators;
+    for (var i = 0; i < operatorREs.length; i++) {
+        var operatorRE = operatorREs[i];
+        var expRE = new RegExp(`^(${lexical.quoteBalanced.source})(${operatorRE.source})(${lexical.quoteBalanced.source})$`);
+        var match = exp.match(expRE);
+        if (match) {
+            var l = evalExp(match[1], scope);
+            var op = syntax.operators[match[2].trim()];
+            var r = evalExp(match[3], scope);
+            return op(l, r);
+        }
+    }
+
+    if (match = exp.match(lexical.rangeLine)) {
+        var low = evalValue(match[1], scope),
+            high = evalValue(match[2], scope) + 1;
+        return _.range(low, high);
+    }
+
+    return evalValue(exp, scope);
+}
+
+function evalValue(str, scope) {
+    str = str && str.trim();
+    if (!str) return undefined;
+
+    if (lexical.isLiteral(str)) {
+        var a = lexical.parseLiteral(str);
+        return lexical.parseLiteral(str);
+    }
+    if (lexical.isVariable(str)) {
+        return scope.get(str);
+    }
+}
+
+function isTruthy(val) {
+    if (val instanceof Array) return !!val.length;
+    return !!val;
+}
+
+function isFalsy(val) {
+    return !isTruthy(val);
+}
+
+module.exports = {
+    evalExp, evalValue, isTruthy, isFalsy
+};