anchor.diff:          if isNull value then
               nullArg argName
   
  +    /// Raises a System.Collections.Generic.KeyNotFoundException.
  +    let [<NoDynamicInvocation>] inline keyNotFound (msg : string) =
  +        raise <| System.Collections.Generic.KeyNotFoundException msg
  +
       /// Not-AND (NAND) of two boolean values.
       /// Returns false when both values are 'true'; otherwise, returns true.
       let [<NoDynamicInvocation>] inline nand (p : bool) (q : bool) =
  
positive.code:     /// The empty string literal.
      let [<Literal>] empty = ""
  
      /// Indicates whether the specified string is null or empty.
      let [<NoDynamicInvocation>] inline isNullOrEmpty str =
          System.String.IsNullOrEmpty str
  
negative.code:     //
      let [<NoDynamicInvocation>] inline ofArray (chars : char[]) =
          System.String (chars)
  
      //
      [<CompiledName("TryFindIndex")>]
      let tryFindIndex (predicate : char -> bool) (str : string) =
          // Preconditions
          checkNonNull "str" str
  
          let len = String.length str
  
          let mutable index = 0
          let mutable foundMatch = false
  
          while index < len && not foundMatch do
              foundMatch <- predicate str.[index]
              index <- index + 1
  
          // Return the index of the matching character, if any.
          if foundMatch then
              Some index
          else None
  
      //
      [<CompiledName("FindIndex")>]
      let findIndex (predicate : char -> bool) (str : string) =
          // Preconditions
          checkNonNull "str" str
  
          // Use tryFindIndex to find the match; raise an exception if one is not found.
          match tryFindIndex predicate str with
          | Some index ->
              index
          | None ->
              // TODO : Return a better error message.
              //keyNotFound ""
              raise <| System.Collections.Generic.KeyNotFoundException ()
  
      //
      [<CompiledName("TryFindIndexOf")>]
      let inline tryFindIndexOf (c : char) (str : string) =
          // Preconditions
          checkNonNull "str" str
  
          match str.IndexOf c with
          | -1 -> None
          | idx -> Some idx
  
      //
      [<CompiledName("FindIndexOf")>]
      let inline findIndexOf (c : char) (str : string) =
          // Preconditions
          checkNonNull "str" str
  
          match str.IndexOf c with
          | -1 ->
              // TODO : Return a better error message.
              //keyNotFound ""
              raise <| System.Collections.Generic.KeyNotFoundException ()
          | idx -> idx
  
      //
      [<CompiledName("TrimStartWith")>]
  