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Why does the compiler expect this type?
f#compiler

I've simplified my problem to the following snippet:

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type IntermediateRecord = (int * list<string>)
type MyData = 
  | Record of IntermediateRecord
  | Records of IntermediateRecord list

let rec ProcessData data =   
  match data with            
  | Record(record) -> ""
  | Records(recs) -> let newList = List.map ProcessData recs  // error on recs

The error for recs reads, "Expecting a MyData list but given a IntermediateRecord list". The function ProcessData has a paramater of type MyData. Why does the compiler think it's of type MyData list?

.

Hello.

In short, because data arg of the ProcessData function does matching for same cases as MyData type has.

If you want to know more you can read following article:
[link:en.wikipedia.org]

You can rewrite your code as:

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//...
 let rec ProcessData data =   
  match data with            
    | Record(record) -> ""
    | Records(recs) ->
      let newList = List.map (fun i -> ProcessData (Record i)) recs //i will be recognised as instance of the IntermediateRecord type
      ""
By on 10/3/2008 11:09 AM ()

Hello.
If you want to know more you can read following article:
[link:en.wikipedia.org]

Wish I could understand it; it's very old and elegant.

Hello.
You can rewrite your code as:

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(fun i -> ProcessData (Record i)) recs

//i will be recognised as instance of the IntermediateRecord type

Thanks; I knew I needed to somehow indicate what the individual items are.

By on 10/3/2008 12:00 PM ()

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