diff --git a/acc.go b/acc.go
index be4fb44..2206bc8 100644
--- a/acc.go
+++ b/acc.go
@@ -14,8 +14,8 @@ type accumulator struct {
 	floating bool
 }
 
-func (a *accumulator) total(vals ...interface{}) (interface{}, error) {
-	if len(vals) == 0 {
+func (a *accumulator) total(vals []interface{}) (interface{}, error) {
+	if vals == nil || len(vals) == 0 {
 		return int64(0), nil
 	}
 
diff --git a/proc.go b/proc.go
index 3936f60..3da45a5 100644
--- a/proc.go
+++ b/proc.go
@@ -4,9 +4,29 @@ import (
 	"errors"
 )
 
-type builtin func(...interface{}) (interface{}, error)
+type builtin func([]interface{}) (interface{}, error)
 
-func addition(vals ...interface{}) (interface{}, error) {
+// evaluates all of the arguments, and then calls the function with the results
+// of the evaluations
+func (b *builtin) call(env *environment, rawArgs []interface{}) (interface{}, error) {
+	if rawArgs == nil {
+		return (*b)(nil)
+	}
+
+	// eval all arguments first
+	args := make([]interface{}, 0, len(rawArgs))
+	for _, raw := range rawArgs {
+		v, err := eval(raw, env)
+		if err != nil {
+			return nil, err
+		}
+		args = append(args, v)
+	}
+
+	return (*b)(args)
+}
+
+func addition(vals []interface{}) (interface{}, error) {
 	a := accumulator{
 		name: "addition",
 		floatFn: func(left, right float64) (float64, error) {
@@ -16,10 +36,10 @@ func addition(vals ...interface{}) (interface{}, error) {
 			return left + right, nil
 		},
 	}
-	return a.total(vals...)
+	return a.total(vals)
 }
 
-func subtraction(vals ...interface{}) (interface{}, error) {
+func subtraction(vals []interface{}) (interface{}, error) {
 	a := accumulator{
 		name: "subtraction",
 		floatFn: func(left, right float64) (float64, error) {
@@ -29,10 +49,10 @@ func subtraction(vals ...interface{}) (interface{}, error) {
 			return left - right, nil
 		},
 	}
-	return a.total(vals...)
+	return a.total(vals)
 }
 
-func multiplication(vals ...interface{}) (interface{}, error) {
+func multiplication(vals []interface{}) (interface{}, error) {
 	a := accumulator{
 		name: "multiplication",
 		floatFn: func(left, right float64) (float64, error) {
@@ -42,10 +62,10 @@ func multiplication(vals ...interface{}) (interface{}, error) {
 			return left * right, nil
 		},
 	}
-	return a.total(vals...)
+	return a.total(vals)
 }
 
-func division(vals ...interface{}) (interface{}, error) {
+func division(vals []interface{}) (interface{}, error) {
 	a := accumulator{
 		name: "division",
 		floatFn: func(left, right float64) (float64, error) {
@@ -61,5 +81,5 @@ func division(vals ...interface{}) (interface{}, error) {
 			return left / right, nil
 		},
 	}
-	return a.total(vals...)
+	return a.total(vals)
 }
diff --git a/skeam.go b/skeam.go
index 0b55184..518dc3b 100644
--- a/skeam.go
+++ b/skeam.go
@@ -131,6 +131,7 @@ func eval(v interface{}, env *environment) (interface{}, error) {
 			return nil, err
 		}
 
+		// check to see if this is a special form
 		if spec, ok := v.(special); ok {
 			if len(t) > 1 {
 				return spec(env, t[1:]...)
@@ -139,33 +140,16 @@ func eval(v interface{}, env *environment) (interface{}, error) {
 			}
 		}
 
-		fn, ok := v.(builtin)
-		if !ok {
-			return nil, fmt.Errorf("expected builtin, found %v", reflect.TypeOf(v))
-		}
-
-		if len(t) > 1 {
-			args := make([]interface{}, 0, len(t)-1)
-			for _, raw := range t[1:] {
-				v, err := eval(raw, env)
-				if err != nil {
-					return nil, err
-				}
-				args = append(args, v)
-			}
-			inner, err := fn(args...)
-			if err != nil {
-				return nil, err
+		// exec builtin func if one exists
+		if b, ok := v.(builtin); ok {
+			if len(t) > 1 {
+				return b.call(env, t[1:])
+			} else {
+				return b.call(env, nil)
 			}
-			return eval(inner, env)
-		}
-
-		inner, err := fn()
-		if err != nil {
-			return nil, err
 		}
 
-		return eval(inner, env)
+		return nil, fmt.Errorf(`expected special form or builtin procedure, received %v`, reflect.TypeOf(v))
 
 	default:
 		return v, nil