diff --git a/eval/builtin_func.go b/eval/builtin_func.go
index 40463b44..ac291f74 100644
--- a/eval/builtin_func.go
+++ b/eval/builtin_func.go
@@ -83,6 +83,8 @@ func init() {
 		&BuiltinFn{"lt", wrapFn(lt)},
 		&BuiltinFn{"gt", wrapFn(gt)},
 
+		&BuiltinFn{"base", wrapFn(base)},
+
 		&BuiltinFn{"=", eq},
 		&BuiltinFn{"deepeq", deepeq},
 
@@ -506,6 +508,20 @@ func gt(ec *EvalCtx, nums ...float64) {
 	}
 }
 
+var ErrBadBase = errors.New("bad base")
+
+func base(ec *EvalCtx, b int, nums ...int) {
+	if b < 2 || b > 36 {
+		throw(ErrBadBase)
+	}
+
+	out := ec.ports[1].Chan
+
+	for _, num := range nums {
+		out <- String(strconv.FormatInt(int64(num), b))
+	}
+}
+
 var ErrNotEqual = errors.New("not equal")
 
 func eq(ec *EvalCtx, args []Value) {
diff --git a/eval/eval_test.go b/eval/eval_test.go
index 8a1824bd..9c9a26da 100644
--- a/eval/eval_test.go
+++ b/eval/eval_test.go
@@ -184,6 +184,7 @@ var evalTests = []struct {
 			String("a"): NewList(strs("1", "2")...)}),
 		String("foo"),
 	}, nomore},
+	{"base 16 42 233", strs("2a", "e9"), nomore},
 }
 
 func strs(ss ...string) []Value {