以 SML 打印到标准输出

Question

datatype term = node of string*term list
         | vnode of string

我有一个 term 类型的值。如何在 SML 中将其打印到标准输出？

Answer 1

您需要先从term 创建一个字符串，然后使用print 打印它。要将term 转换为字符串，您可以定义如下函数：

fun termToString (node (str, terms)) =
    "node(" ^ str ^ ", " ^ termListToString terms ^ ")"
  | termToString (vnode str) =
    "vnode(" ^ str ^ ")"
and termListToString terms =
    "[" ^ String.concatWith ", " (map termToString terms) ^ "]"