added "begin" special form

input.scm

@@ -42,3 +42,13 @@ x
 (plusone 1)
 
 ((lambda (x) (* x x)) 4)
+
+((lambda (x y) (+ x y)) 10 25)
+
+(define make-account
+  (lambda (balance)
+    (lambda (amt)
+      (begin (set! balance (+ balance amt)) balance))))
+
+(define a1 (make-account 100.00))
+(a1 -20.00)

skeam.go

@@ -32,6 +32,7 @@ var universe = &environment{map[symbol]interface{}{
 	"if":     special(_if),
 	"set!":   special(set),
 	"lambda": special(mklambda),
+	"begin":  special(begin),
 }, nil}
 
 // parses the string lexeme into a value that can be eval'd

special.go

@@ -187,3 +187,18 @@ func mklambda(env *environment, args ...interface{}) (interface{}, error) {
 
 	return lambda{env, arglabels, body}, nil
 }
+
+func begin(env *environment, args ...interface{}) (interface{}, error) {
+	debugPrint("begin")
+
+	var err error
+	var v interface{}
+	for _, arg := range args {
+		v, err = eval(arg, env)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return v, nil
+}