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| 1 | +module TaskSeq.Tests.FoldWhile |
| 2 | + |
| 3 | +open Xunit |
| 4 | +open FsUnit.Xunit |
| 5 | + |
| 6 | +open FSharp.Control |
| 7 | + |
| 8 | +// |
| 9 | +// TaskSeq.foldWhile |
| 10 | +// TaskSeq.foldWhileAsync |
| 11 | +// |
| 12 | +// Semantics match TaskSeq.takeWhile: the predicate is evaluated against (state, element) |
| 13 | +// before that element is folded in. When the predicate returns false, iteration halts |
| 14 | +// without folding that element, and no further elements are enumerated. |
| 15 | +// |
| 16 | + |
| 17 | +module EmptySeq = |
| 18 | + [<Fact>] |
| 19 | + let ``Null source is invalid`` () = |
| 20 | + assertNullArg |
| 21 | + <| fun () -> TaskSeq.foldWhile (fun _ _ -> true) (fun _ item -> item + 1) 0 null |
| 22 | + |
| 23 | + assertNullArg |
| 24 | + <| fun () -> TaskSeq.foldWhileAsync (fun _ _ -> Task.fromResult true) (fun _ item -> Task.fromResult (item + 1)) 0 null |
| 25 | + |
| 26 | + [<Theory; ClassData(typeof<TestEmptyVariants>)>] |
| 27 | + let ``TaskSeq-foldWhile returns initial state when empty`` variant = task { |
| 28 | + let! result = |
| 29 | + Gen.getEmptyVariant variant |
| 30 | + |> TaskSeq.foldWhile (fun _ _ -> true) (fun _ item -> item + 1) -1 |
| 31 | + |
| 32 | + result |> should equal -1 |
| 33 | + } |
| 34 | + |
| 35 | + [<Theory; ClassData(typeof<TestEmptyVariants>)>] |
| 36 | + let ``TaskSeq-foldWhileAsync returns initial state when empty`` variant = task { |
| 37 | + let! result = |
| 38 | + Gen.getEmptyVariant variant |
| 39 | + |> TaskSeq.foldWhileAsync (fun _ _ -> Task.fromResult true) (fun _ item -> Task.fromResult (item + 1)) -1 |
| 40 | + |
| 41 | + result |> should equal -1 |
| 42 | + } |
| 43 | + |
| 44 | + [<Theory; ClassData(typeof<TestEmptyVariants>)>] |
| 45 | + let ``TaskSeq-foldWhile does not call predicate or folder when empty`` variant = task { |
| 46 | + let mutable predicateCalled = false |
| 47 | + let mutable folderCalled = false |
| 48 | + |
| 49 | + let! _ = |
| 50 | + Gen.getEmptyVariant variant |
| 51 | + |> TaskSeq.foldWhile |
| 52 | + (fun _ _ -> |
| 53 | + predicateCalled <- true |
| 54 | + true) |
| 55 | + (fun state _ -> |
| 56 | + folderCalled <- true |
| 57 | + state) |
| 58 | + 0 |
| 59 | + |
| 60 | + predicateCalled |> should be False |
| 61 | + folderCalled |> should be False |
| 62 | + } |
| 63 | + |
| 64 | + [<Theory; ClassData(typeof<TestEmptyVariants>)>] |
| 65 | + let ``TaskSeq-foldWhileAsync does not call predicate or folder when empty`` variant = task { |
| 66 | + let mutable predicateCalled = false |
| 67 | + let mutable folderCalled = false |
| 68 | + |
| 69 | + let! _ = |
| 70 | + Gen.getEmptyVariant variant |
| 71 | + |> TaskSeq.foldWhileAsync |
| 72 | + (fun _ _ -> task { |
| 73 | + predicateCalled <- true |
| 74 | + return true |
| 75 | + }) |
| 76 | + (fun state _ -> task { |
| 77 | + folderCalled <- true |
| 78 | + return state |
| 79 | + }) |
| 80 | + 0 |
| 81 | + |
| 82 | + predicateCalled |> should be False |
| 83 | + folderCalled |> should be False |
| 84 | + } |
| 85 | + |
| 86 | +module Functionality = |
| 87 | + [<Fact>] |
| 88 | + let ``TaskSeq-foldWhile with always-true predicate behaves like fold`` () = task { |
| 89 | + let! result = |
| 90 | + TaskSeq.ofList [ 1; 2; 3; 4; 5 ] |
| 91 | + |> TaskSeq.foldWhile (fun _ _ -> true) (fun acc item -> acc + item) 0 |
| 92 | + |
| 93 | + result |> should equal 15 |
| 94 | + } |
| 95 | + |
| 96 | + [<Fact>] |
| 97 | + let ``TaskSeq-foldWhileAsync with always-true predicate behaves like foldAsync`` () = task { |
| 98 | + let! result = |
| 99 | + TaskSeq.ofList [ 1; 2; 3; 4; 5 ] |
| 100 | + |> TaskSeq.foldWhileAsync (fun _ _ -> Task.fromResult true) (fun acc item -> Task.fromResult (acc + item)) 0 |
| 101 | + |
| 102 | + result |> should equal 15 |
| 103 | + } |
| 104 | + |
| 105 | + [<Fact>] |
| 106 | + let ``TaskSeq-foldWhile is left-associative like fold`` () = task { |
| 107 | + let! result = |
| 108 | + TaskSeq.ofList [ "b"; "c"; "d" ] |
| 109 | + |> TaskSeq.foldWhile (fun _ _ -> true) (fun acc item -> acc + item) "a" |
| 110 | + |
| 111 | + result |> should equal "abcd" |
| 112 | + } |
| 113 | + |
| 114 | + [<Fact>] |
| 115 | + let ``TaskSeq-foldWhileAsync is left-associative like foldAsync`` () = task { |
| 116 | + let! result = |
| 117 | + TaskSeq.ofList [ "b"; "c"; "d" ] |
| 118 | + |> TaskSeq.foldWhileAsync (fun _ _ -> Task.fromResult true) (fun acc item -> Task.fromResult (acc + item)) "a" |
| 119 | + |
| 120 | + result |> should equal "abcd" |
| 121 | + } |
| 122 | + |
| 123 | +module Halt = |
| 124 | + [<Fact>] |
| 125 | + let ``TaskSeq-foldWhile stops immediately when predicate is false on first element`` () = task { |
| 126 | + let mutable predicateCalls = 0 |
| 127 | + let mutable folderCalls = 0 |
| 128 | + |
| 129 | + let! result = |
| 130 | + TaskSeq.ofList [ 1; 2; 3; 4; 5 ] |
| 131 | + |> TaskSeq.foldWhile |
| 132 | + (fun _ _ -> |
| 133 | + predicateCalls <- predicateCalls + 1 |
| 134 | + false) |
| 135 | + (fun _ item -> |
| 136 | + folderCalls <- folderCalls + 1 |
| 137 | + item) |
| 138 | + 0 |
| 139 | + |
| 140 | + result |> should equal 0 |
| 141 | + predicateCalls |> should equal 1 |
| 142 | + folderCalls |> should equal 0 |
| 143 | + } |
| 144 | + |
| 145 | + [<Fact>] |
| 146 | + let ``TaskSeq-foldWhileAsync stops immediately when predicate is false on first element`` () = task { |
| 147 | + let mutable predicateCalls = 0 |
| 148 | + let mutable folderCalls = 0 |
| 149 | + |
| 150 | + let! result = |
| 151 | + TaskSeq.ofList [ 1; 2; 3; 4; 5 ] |
| 152 | + |> TaskSeq.foldWhileAsync |
| 153 | + (fun _ _ -> task { |
| 154 | + predicateCalls <- predicateCalls + 1 |
| 155 | + return false |
| 156 | + }) |
| 157 | + (fun _ item -> task { |
| 158 | + folderCalls <- folderCalls + 1 |
| 159 | + return item |
| 160 | + }) |
| 161 | + 0 |
| 162 | + |
| 163 | + result |> should equal 0 |
| 164 | + predicateCalls |> should equal 1 |
| 165 | + folderCalls |> should equal 0 |
| 166 | + } |
| 167 | + |
| 168 | + [<Fact>] |
| 169 | + let ``TaskSeq-foldWhile halts mid-sequence without folding the halting element`` () = task { |
| 170 | + // Sum while adding the next element would keep the total <= 5. Once adding |
| 171 | + // the element would overshoot, stop — that element is NOT folded in. |
| 172 | + let mutable predicateCalls = 0 |
| 173 | + let mutable folderCalls = 0 |
| 174 | + |
| 175 | + let! result = |
| 176 | + TaskSeq.ofList [ 1; 2; 3; 4; 5 ] |
| 177 | + |> TaskSeq.foldWhile |
| 178 | + (fun acc item -> |
| 179 | + predicateCalls <- predicateCalls + 1 |
| 180 | + acc + item <= 5) |
| 181 | + (fun acc item -> |
| 182 | + folderCalls <- folderCalls + 1 |
| 183 | + acc + item) |
| 184 | + 0 |
| 185 | + |
| 186 | + // 1 (ok, total 1), 2 (ok, total 3), 3 (would make 6 > 5, stop) |
| 187 | + result |> should equal 3 |
| 188 | + predicateCalls |> should equal 3 |
| 189 | + folderCalls |> should equal 2 |
| 190 | + } |
| 191 | + |
| 192 | + [<Fact>] |
| 193 | + let ``TaskSeq-foldWhileAsync halts mid-sequence without folding the halting element`` () = task { |
| 194 | + let mutable predicateCalls = 0 |
| 195 | + let mutable folderCalls = 0 |
| 196 | + |
| 197 | + let! result = |
| 198 | + TaskSeq.ofList [ 1; 2; 3; 4; 5 ] |
| 199 | + |> TaskSeq.foldWhileAsync |
| 200 | + (fun acc item -> task { |
| 201 | + predicateCalls <- predicateCalls + 1 |
| 202 | + return acc + item <= 5 |
| 203 | + }) |
| 204 | + (fun acc item -> task { |
| 205 | + folderCalls <- folderCalls + 1 |
| 206 | + return acc + item |
| 207 | + }) |
| 208 | + 0 |
| 209 | + |
| 210 | + result |> should equal 3 |
| 211 | + predicateCalls |> should equal 3 |
| 212 | + folderCalls |> should equal 2 |
| 213 | + } |
| 214 | + |
| 215 | + [<Fact>] |
| 216 | + let ``TaskSeq-foldWhile does not enumerate past the halting element`` () = task { |
| 217 | + // Source has a side effect per pulled element; halt on the 3rd pull. |
| 218 | + let mutable pulled = 0 |
| 219 | + |
| 220 | + let source = taskSeq { |
| 221 | + for i in 1..5 do |
| 222 | + pulled <- pulled + 1 |
| 223 | + yield i |
| 224 | + } |
| 225 | + |
| 226 | + let! _ = |
| 227 | + source |
| 228 | + |> TaskSeq.foldWhile (fun _ item -> item < 3) (fun acc item -> acc + item) 0 |
| 229 | + |
| 230 | + // Pull 1 (ok), pull 2 (ok), pull 3 (predicate false, stop) — must not pull 4. |
| 231 | + pulled |> should equal 3 |
| 232 | + } |
| 233 | + |
| 234 | + [<Fact>] |
| 235 | + let ``TaskSeq-foldWhileAsync does not enumerate past the halting element`` () = task { |
| 236 | + let mutable pulled = 0 |
| 237 | + |
| 238 | + let source = taskSeq { |
| 239 | + for i in 1..5 do |
| 240 | + pulled <- pulled + 1 |
| 241 | + yield i |
| 242 | + } |
| 243 | + |
| 244 | + let! _ = |
| 245 | + source |
| 246 | + |> TaskSeq.foldWhileAsync (fun _ item -> Task.fromResult (item < 3)) (fun acc item -> Task.fromResult (acc + item)) 0 |
| 247 | + |
| 248 | + pulled |> should equal 3 |
| 249 | + } |
| 250 | + |
| 251 | + [<Fact>] |
| 252 | + let ``TaskSeq-foldWhile that never halts is equivalent to fold`` () = task { |
| 253 | + let! result = |
| 254 | + TaskSeq.ofList [ 1; 2; 3; 4; 5 ] |
| 255 | + |> TaskSeq.foldWhile (fun _ item -> item <= 10) (fun acc item -> acc + item) 0 |
| 256 | + |
| 257 | + result |> should equal 15 |
| 258 | + } |
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