Make sure all arguments get evaluated

src/evaluator.js

     let evaluatedTree = []
 
     tree.forEach(node => {
-      let evaluatedNode = this.evalNode(node)
+      let evaluatedNode = this.evalNode(node, env)
 
       if (evaluatedNode) {
         if (evaluatedNode.constructor === OsloError) {
             return this.evalNode(
               new AST.Application({
                 function: env.get(node.function),
-                args: node.args,
+                args: this.eval(node.args, env),
               }),
               env,
             )
 
             return this.evalNode(node.function.body, innerEnv)
           case Function:
-            let args = node.args.map(arg => {
-              return this.evalNode(arg, env)
-            })
+            let args = this.eval(node.args, env)
             args.unshift(this)
             return node.function.call(...args)
         }

test/evaluatorTest.js

     new OsloError({ line: 1, message: "Symbol 'x' is not bound" }),
   )
 })
+
+test('factorial', t => {
+  t.plan(1)
+
+  const tree = helpers.evaluate(`
+    (define factorial
+      (lambda (x)
+        (if (= x 0)
+          1
+          (* x (factorial (- x 1))))))
+    (factorial 5)
+
+  `)
+  t.deepEqual(tree[0], new AST.Number({ value: 120 }))
+})