#light

module Nine

printfn "%A" (
 match 1+1 with                        // p. 134
   |  3 -> "three"
   |  2 -> "two"
   |  _ -> "hmm"
 )
printfn "%A" ((fun x -> x+2) 1)

let rec split = function
   | ([], lt, pivot) -> ([],[])
   | (x::xs, lt, pivot) ->
       let (below,above) = split(xs, lt, pivot)
       if lt(x,pivot) then (x::below,above)
       else (below, x::above)
let rec quicksort = function
  | ([], lt) -> []
  | (pivot::rest, lt) ->
      let (below, above) = split(rest, lt, pivot)
      quicksort(below,lt)@[pivot]
          @quicksort(above,lt)
let intBefore(a,b)  = a<b;                          // p. 137
printfn "%A" (quicksort([1;4;3;2;5], intBefore))    
printfn "%A" (quicksort([1;4;3;2;5],fun (a,b) -> a<b))
printfn "%A" (quicksort([1;4;3;2;5],fun (a,b) -> a>b))  
let f (a, b) = a + b;                               // p. 138
printfn "%A" (f (2,3))
let g a = fun b -> a+b
printfn "%A" (g 2 3)
let add2 = g 2;                                     // p. 139
printfn "%A" (add2 3)
let h a b = a + b
printfn "%A" (h 2 3)     
printfn "%A" (List.map not [true; false])           // p. 140
printfn "%A" (List.map (fun x->x+1) [1;2;3;4])
printfn "%A" (List.map ((+) 1) [1;2;3;4])
printfn "%A" (List.map (fun x->x%2=0) [1;2;3;4])
printfn "%A" (List.map (fun (a,b)->a+b) [(1,2);(3,4)])
let f1 = List.map (fun (a,b)->a+b)                  // p. 141
printfn "%A" (f1 [(1,2);(3,4)])
printfn "%A" (List.fold_right (+) [1;2;3;4] 0)
   // F# fold_right signature is different than ML
printfn "%A" (List.fold_right (*) [1;2;3;4] 1)
printfn "%A" (List.fold_right (+) ["abc";"def";"ghi"] "")
printfn "%A" (List.fold_right (fun a b -> a::b) [1;2;3;4] [5])
let addup = List.fold_left (+) 0                    // p. 142
printfn "%A" (addup [1;2;3;4;5])
let thin L = List.fold_right (fun a b -> 
                  if a<0 then b else a::b) L []     // p. 143 
printfn "%A" (thin [-1;2;-3;4;-5;6])
printfn "%A" (List.fold_left (+) 0 [1;2;3;4])
printfn "%A" (List.fold_left (*) 1 [1;2;3;4])
printfn "%A" (List.fold_right (-) [1;2;3;4] 0)
printfn "%A" (List.fold_left (-) 0 [1;2;3;4])
   // (((0-1)-2)-3)-4 not 4-(3-(2-(1-0)))
printfn "%A" (List.fold_left (+) "" ["abc";"def";"ghi"])