haskell - 您的 FFI 声明需要类型签名

Question

有时我会遇到奇怪的问题，请考虑以下示例:

编译:

renderFrame :: Frame -> Fay ()
renderFrame frame = do
     stack <- getStack
     if length stack > 0
           then (do
                   let e = head stack
                   traceEventCoord e)
           else (do return ())
     reqFrame renderFrame
     emptyStack
     where traceEventCoord :: Event -> Fay ()
           traceEventCoord e = do
               eX <- pageX e
               eY <- pageY e
               let str = show eX ++ " x " ++ show eY
               trace <- elById "trace"
               if isNull trace
                   then return ()
                   else elSetHtml (fromNullable trace) str


pageX :: Event -> Fay Int
pageX = ffi "%1['pageX']"

pageY :: Event -> Fay Int
pageY = ffi "%1['pageY']"

它也是:

getParentGroups :: Fragment -> Fay [Fragment]
getParentGroups f = do
    p <- getParent f
    nn <- nodeName (fromNullable p)
    return [fromNullable p]

getParent :: Fragment -> Fay (Nullable Fragment)
getParent = ffi "%1.parent()"
nodeName :: Fragment -> Fay String
nodeName = ffi "%1.node.nodeName"

但是，如果我将辅助函数放在 where block 中，则会出现编译错误:

fay: your FFI declaration needs a type signature pageX = ffi "%1['pageX']" fay: your FFI declaration needs a type signature: getParent = ffi "%1.parent()"

例如

-- ...
where traceEventCoord :: Event -> Fay ()
      traceEventCoord e = do
          eX <- pageX e
          eY <- pageY e
          let str = show eX ++ " x " ++ show eY
          trace <- elById "trace"
          if isNull trace
              then return ()
              else elSetHtml (fromNullable trace) str
       pageX :: Event -> Fay Int
       pageX = ffi "%1['pageX']"
       pageY :: Event -> Fay Int
       pageY = ffi "%1['pageY']"

和

getParentGroups f = do
    p <- getParent f
    nn <- nodeName (fromNullable p)
    return [fromNullable p]
    where
        getParent :: Fragment -> Fay (Nullable Fragment)    
        getParent = ffi "%1.parent()"
        nodeName :: Fragment -> Fay String
        nodeName = ffi "%1.node.nodeName"

请注意，第一个示例中的 traceEventCoords 不会引发此问题。是错误吗？

附言第二个例子只是一个例子，最终代码会重构一点，但它适用于演示目的。

Answer 1

更新:已在 fay 0.19 中实现并发布

抱歉耽搁了!时差让我 :(

我认为这还没有实现。最初只在顶层支持 ffi，然后添加了 ffi 表达式，它需要表达式 ffi "alert('foo')"::Fay () 旁边的类型签名。我认为没有人会为 where 语句也这样做。