read-eval-print-loop - idris REPL : creating function

Question

如何在 Idris REPL 中编写函数？如果我输入函数定义 longer: string -> string -> string在 REPL 中，我收到以下错误消息:

(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有你需要的例子。您应该使用 :let命令。像这样:

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 不会做任何智能操作，当您输入函数类型时，它不会进入一些智能多行模式。 :let命令用于定义 REPL 中的任何顶级绑定(bind)。

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 .