Need Help Understanding & Correcting "missing parameter type for expanded function"

I hope that the following explanation helps:   placeholder syntax like: someFunction(someArg, _, otherArg) is equivalent with: (arg) => someFunction(someArg, arg, otherArg) if the type inferencer does not have enough context information to infer the type, say A, of arg, then you have to help it as follows: (arg: A) => someFunction(someArg, arg, otherArg)   -- sometimes you have to give the inferencer a helping hand
  Luc
On Mon, Mar 23, 2009 at 3:08 PM, Randall R Schulz <rschulz@sonic.net> wrote:

Hi,

I'm trying to understand and resolve these errors:

/dar/rho/src/rho/alg/Traversals.scala
   Error:Error:line (324)error: missing parameter type for expanded function
     ((x$12) => ExpressionCursor(expr, next.node.pos.ahead(), x$12, next.node.pol)) _, next.node.pol)))


The code is:

   traversal ++ connected.map(TraversalAction(ahead, ExpressionCursor(expr, next.node.pos.ahead(), _, next.node.pol)))


A similar fragment:

   traversal ++ next.at.asInstanceOf[FunctionTerm].args.map(ExpressionCursor(expr, next.pos.ahead(), _, next.pol))

Does not prodduce this error.


TraversalAction and ExpressionCursor are a case-class constructors.

I gather the problem has to do with the anonymous function parameter
being nested inside the second constructor the erroneous case, but
don't know how to resolve it.


Randall Schulz

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reality goes far beyond imagination

On Monday March 23 2009, Randall R Schulz wrote:
> Hi,
>
> I'm trying to understand and resolve these errors:
>
> /dar/rho/src/rho/alg/Traversals.scala
> Error:Error:line (324)error: missing parameter type for expanded function
> ((x$12) => ExpressionCursor(expr, next.node.pos.ahead(), x$12, next.node.pol)) _, next.node.pol)))
>
>
> The code is:
>
> traversal ++ connected.map(TraversalAction(ahead, ExpressionCursor(expr, next.node.pos.ahead(), _, next.node.pol)))
>
> ...
>
> TraversalAction and ExpressionCursor are a case-class constructors.
>
> I gather the problem has to do with the anonymous function parameter
> being nested inside the second constructor the erroneous case, but
> don't know how to resolve it.

On a hunch, I changed the code thusly:

traversal ++ connected.map(arg => TraversalAction(ahead, ExpressionCursor(expr, next.node.pos.ahead(), arg, next.node.pol)))

And it compiled. What did I do?

Randall Schulz