Idris REPL:创建函数

Question

如何在Idris REPL中编写函数？如果我在REPL中输入函数定义longer: string -> string -> string，我会得到以下错误信息：

(input):1:7: error: expected: "$",
    "&&", "*", "*>", "+", "++", "-",
    "->", ".", "/", "/=", "::", "<",
    "<$>", "<*", "<*>", "<+>", "<<",
    "<=", "<==", "<|>", "=", "==",
    ">", ">=", ">>", ">>=", "\\\\",
    "`", "|", "||", "~=~",
    ambiguous use of a left-associative operator,
    ambiguous use of a non-associative operator,
    ambiguous use of a right-associative operator,
    end of input, function argument
longer: string -> string -> string<EOF>
      ^

Answer 1

Idris documentation提供了您所需的示例。您应该使用:let命令。如下所示：

Idris> :let longer : String -> String -> String; longer s1 s2 = if length s1 > length s2 then s1 else s2
Idris> longer "abacaba" "abracadabra"
"abracadabra" : String

默认情况下，Idris REPL不会执行任何智能操作，当您输入函数类型时，它不会进入智能多行模式。:let命令用于在REPL中定义任何顶级绑定。

另一个时刻:如果你想使用字符串类型，你应该使用String (以大写字母开头)而不是string。