将OCaml字符串转换为format6 [英] Converting OCaml strings to format6

问题描述

以下代码无法编译:

let x = "hello" in
Printf.printf x

错误是:

Error: This expression has type string but an expression was expected of type
     ('a, out_channel, unit) format =
       ('a, out_channel, unit, unit, unit, unit) format6

1)有人可以对错误消息进行解释吗?

1) Can someone give an explanation of the error message?

2)为什么不能将字符串传递给printf?

2) And why would a string cannot be passed to printf ?

推荐答案

printf的第一个参数的类型必须为('a, out_channel, unit) format，而不是字符串.字符串文字可以自动转换为适当的格式类型，但是字符串通常不能.

The first argument to printf must be of type ('a, out_channel, unit) format not string. String literals can be automatically converted to an appropriate format type, but strings in general can't.

其原因是格式字符串的确切类型取决于字符串的内容.例如，表达式printf "%d-%d"的类型应为int -> int -> ()，而printf "%s"的类型应为string -> ().显然，当在编译时不知道格式字符串时，这种类型的检查是不可能的.

The reason for that is that the exact type of a format string depends on the contents of the string. For example the type of the expression printf "%d-%d" should be int -> int -> () while the type of printf "%s" should be string -> (). Clearly such type checking is impossible when the format string is not known at compile time.

根据您的情况，您可以执行printf "%s" x.

In your case you can just do printf "%s" x.

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