"Undefined name" 对于存在于 where 外部范围内的值

Question

我想使用在 where 子句的外部范围内定义的值，就像这样

foo : Nat
foo = case Just 1 of
  Nothing => 0
  Just x => bar where
    bar : Nat
    bar = x

但我得到了

Error: While processing right hand side of foo. While processing right hand side of foo,bar. Undefined name x. 

Foo.idr:30:11--30:12
    |
 30 |     bar = x

鉴于 the docs

中的内容，我不明白

Any names which are visible in the outer scope are also visible in the where clause (unless they have been redefined, such as xs here). A name which appears in the type will be in scope in the where clause.

将 x 绑定到 RHS 上的新名称

foo : Nat
foo = case Just 1 of
  Nothing => 0
  Just x => let x' = x in bar where
    bar : Nat
    bar = x'

对于 bar = x'

产生类似的错误 Undefined name x'

Answer 1

您似乎在寻找 let 而不是 where。外部范围意味着 foo.

的参数

"Undefined name" 对于存在于 where 外部范围内的值

"Undefined name" for value present in outer scope of where

scope

idris