added "let"

index.js

@@ -63,6 +63,9 @@ let methods = {
     },
     '-':function(args) {
         let end_args = args.map(arg=>handle(arg))
+        if(end_args.length == 1) {
+            return -end_args[0]
+        }
         return end_args.reduce(function(acc,cur) {
             return acc - cur
         })
@@ -75,6 +78,9 @@ let methods = {
     },
     '/':function(args) {
         let end_args = args.map(arg=>handle(arg))
+        if(end_args.length == 1) {
+            return 1/end_args[0]
+        }
         return end_args.reduce(function(acc,cur) {
             return acc / cur
         })
@@ -186,6 +192,18 @@ let methods = {
             return ret
         }
     },
+    'let':function(args) {
+        let params = args[0]
+        let prog = args[1]
+        let old_base = JSON.stringify(base)
+        for(let param of params) {
+            handle(['define',param[0],param[1]])
+        }
+        let ret = handle(prog)
+        base = JSON.parse(old_base)
+        return ret
+
+    },
     'exit':function(args) {
         process.exit(0)
     }

test.js

@@ -81,4 +81,11 @@ test('negate', t => {
     t.is(scheme("a"), true)
     t.is(scheme("b"), false)
     t.is(scheme("(not b)"), true)
+})
+
+test('let', t => {
+    scheme('(clear)')
+    scheme("(define func (lambda (n) (let ((a 5)) (- a n))))")
+    t.is(scheme("(func 5)"), 0)
+    t.is(scheme("(func (- 5))"), 10)
 })