generics - 保持部分应用的函数通用

Question

是否可以部分应用诸如 bprintf 之类的功能？并防止它因最初使用而受到限制？

我想做以下事情:

let builder = new System.Text.StringBuilder()
let append = Printf.bprintf builder
append "%i" 10
append "%s" string_value

Answer 1

导致这种情况的 F# 方面称为值限制。你可以看到，如果你只输入两个 let对 F# Interactive 的声明(以便编译器不会从第一次使用中推断出类型):

> let builder = new System.Text.StringBuilder() 
  let append = Printf.bprintf builder ;;

error FS0030: Value restriction. The value 'append' has been inferred to have generic type val append : ('_a -> '_b) when '_a :> Printf.BuilderFormat<'_b> Either make the arguments to 'append' explicit or, if you do not intend for it to be generic, add a type annotation.

有一个 excellent article by Dmitry Lomov来自 F# 团队的详细解释。正如文章所建议的，一种解决方案是添加显式类型参数声明:

let builder = new System.Text.StringBuilder() 
let append<'T> : Printf.BuilderFormat<'T> -> 'T = Printf.bprintf builder 
append "%i" 10 
append "%s" "Hello"

这将工作得很好。