MapReduce WordCount

#light
 
namespace Microsoft.MapReduce
 
[<CompilationRepresentation(CompilationRepresentationFlags.ModuleSuffix)>]
[<CompilationMapping(SourceConstructFlags.Module)>]
module String =
  open System.Text.RegularExpressions
  
  let words (s:string) : string list =
    [for m in Regex.Matches(s, @"\w+") -> m.Value]
 
[<CompilationRepresentation(CompilationRepresentationFlags.ModuleSuffix)>]
[<CompilationMapping(SourceConstructFlags.Module)>]
[<AutoOpen>]
module Operators =
  let const x _ = x
 
[<CompilationRepresentation(CompilationRepresentationFlags.ModuleSuffix)>]
[<CompilationMapping(SourceConstructFlags.Module)>]
module Tuple =
  let uncurry f p = f (fst p) (snd p)
 
[<CompilationRepresentation(CompilationRepresentationFlags.ModuleSuffix)>]
[<CompilationMapping(SourceConstructFlags.Module)>]
module Map =
  let insert_with (f:'a -> 'a -> 'a) (kx:'k) (x:'a) (t:Map<'k,'a>) : Map<'k, 'a> =
    match Map.tryfind kx t with
    | None -> Map.add kx x t
    | Some v -> t |> Map.remove kx |> Map.add kx (f v x)
 
module WordCount =
  let map_reduce m r =
    let map_per_key : Map<'k1, 'v1> -> ('k2 * 'v2) list =
      Map.to_list >> List.map (Tuple.uncurry m) >> List.concat
  
    let group_by_key (l:('k2 * 'v2) list) : Map<'k2,'v2 list> =
      let insert d (k2, v2) = Map.insert_with (@) (k2) [v2] d
      l |> List.fold_left insert Map.empty
 
    let reduce_per_key : Map<'k2, 'v2 list> -> Map<'k2,'v3> =
      let unSome k (Some v) = v
      let isSome k = function
        | Some _ -> true
        | None -> false
      Map.mapi r >> Map.filter isSome >> Map.mapi unSome
    
    map_per_key >> group_by_key >> reduce_per_key
    
  let word_occurrence_count : Map<string, string> -> Map<string, int> =
    let m = const (String.words >> List.map(fun s -> (s, 1)))
    let r = const (List.sum >> Some)
    map_reduce m r
 
module MainModule =
  [<EntryPoint>]
  let main(args:string array) =
    printfn "%A"
      (WordCount.word_occurrence_count
        (Map.empty
          |> Map.add "doc1" "appreciate the unfold"
          |> Map.add "doc2" "fold the fold"))
    0