OCaml构造函数解包

Question

是否可以通过将其数据绑定到单个值而不是元组来解压缩类型？

# type foo = Foo of int * string;;
type foo = Foo of int * string
# Foo (3; "bar");;
  Foo (3; "bar");;
Error: The constructor Foo expects 2 argument(s),
       but is applied here to 1 argument(s)
# Foo (3, "bar");;
- : foo = Foo (3, "bar")

# (* Can this possibly work? *)
# let Foo data = Foo (3, "bar");;
  let Foo data = Foo (3, "bar");;
Error: The constructor Foo expects 2 argument(s),
       but is applied here to 1 argument(s)

# (* Here is the version that I know works: *)
# let Foo (d1, d2) = Foo (3, "bar");;
val d1 : int = 3
val d2 : string = "bar"

这在语法上是否可行？

Answer 1

这是OCaml语法的一个棘手部分.如果在显示时定义类型,则其构造函数Foo需要括号中的两个值.它总是必须是两个值,它不是单个值,而是一个元组.

如果您愿意使用其他类型,您可以做更符合您想要的事情:

# type bar = Bar of (int * string);;
type bar = Bar of (int * string)
# let Bar data = Bar (3, "foo");;
val data : int * string = (3, "foo")
# let Bar (d1, d2) = Bar (3, "foo");;
val d1 : int = 3
val d2 : string = "foo"

当以这种方式声明时,构造函数Bar需要一个值为元组的值.这可以更灵活,但它也需要更多的内存来表示它,并且访问部件需要更长的时间.