Idris REPL:创建功能

时间:2017-07-12 10:14:31

标签: read-eval-print-loop idris

如何在Idris REPL中编写函数?如果我在REPL中键入函数定义longer: string -> string -> string,则会收到以下错误消息:

(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>
      ^

1 个答案:

答案 0 :(得分:7)

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,当您输入功能类型时,它不会进入某些智能多线模式。 :let命令用于定义REPL中的任何顶级绑定。

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