Minor refactoring: x = null to isNull x, and faster nicePascalName

https://latkin.org/blog/2015/05/18/null-checking-considerations-in-f-its-harder-than-you-think/

docs/content/samples/presidents.fsx

@@ -85,7 +85,7 @@ let presidentTerms =
     if string pos.``Basic title`` = "President" then
       // Get start and end year of the position
       let starty = DateTime.Parse(pos.From).Year
-      let endy = if pos.To = null then 2013 else
+      let endy = if isNull pos.To then 2013 else
                    DateTime.Parse(pos.To).Year
       // Get their party
       let dem = pres.Party |> Seq.exists (fun p -> p.Party.Name = "Democratic Party")

docs/tools/formatters.fsx

@@ -63,7 +63,7 @@ open FSharp.Charting.ChartTypes
 /// Extract values from any series using reflection
 let (|SeriesValues|_|) (value:obj) = 
   let iser = value.GetType().GetInterface("ISeries`1")
-  if iser <> null then
+  if not (isNull iser) then
     let keys = value.GetType().GetProperty("Keys").GetValue(value) :?> System.Collections.IEnumerable
     let vector = value.GetType().GetProperty("Vector").GetValue(value) :?> IVector
     Some(Seq.zip (Seq.cast<obj> keys) vector.ObjectSequence)

src/Deedle.Excel/Excel.fs

@@ -1,4 +1,4 @@
-module Deedle.Excel
+module Deedle.Excel
 
 open Deedle
 
@@ -87,21 +87,21 @@ let openNewExcelApplication () =
     excelApp
 
 let private assertInstance () =
-    if excelApp <> null then
+    if not (isNull excelApp) then
         let wbs = excelApp.Workbooks
         if wbs.Count = 0 then
             wbs.Add(Enums.XlWBATemplate.xlWBATWorksheet) |> ignore
 
-        if excelApp = null then
+        if isNull excelApp then
             openNewExcelApplication () |> ignore
-        elif activeWb <> null then
+        elif not (isNull activeWb) then
             activeWb.Activate()
 
 let private openWorkbook (readonly : bool) filename =
     excelApp.get_Workbooks().Open(filename, null, readonly)
 
 let getActiveWorkbook () =
-    if activeWb = null then
+    if isNull activeWb then
         excelApp.ActiveWorkbook
     else
         activeWb
@@ -146,7 +146,7 @@ let getRealRange (range : obj) =
     assertInstance ()
     match range with
     | :? string as str ->
-        let idx = str.IndexOf("!")
+        let idx = str.IndexOf '!'
         if idx > 0 then switchSheet (str.Substring(0, idx))
     |  _ -> ()
     excelApp.Range(range)
@@ -171,7 +171,7 @@ let private unionRanges r1 r2 =
     RealExcel (excelApp.Union(real1, real2))
 
 let private putArray isH (arr : obj [,]) startRange =
-    if arr = null || Array2D.length1 arr = 0 || Array2D.length2 arr = 0 then
+    if isNull arr || Array2D.length1 arr = 0 || Array2D.length2 arr = 0 then
         startRange
     else
         let (height, width) = arr |> arraySize
@@ -330,7 +330,7 @@ module internal XlHelper =
                 |> aptest showCols (putArray false t.ColumnHeaders)
                 |> putArray false t.DataArray
                 |> aptest showRows (moveLeftCols 1 >> skipHistory 1)
-                |> aptest (tableStyle <> null) (applyToHistory (fun r->
+                |> aptest (not (isNull tableStyle)) (applyToHistory (fun r->
                     ExcelStyles.ApplyTableStyle(r,tableStyle, showFilter, showRows)))
 
     // ----------------------------------------------------------------------------------------
@@ -361,7 +361,7 @@ module internal XlHelper =
       | _ -> box ""
 
     let formatExcelHeader (value:obj) =
-      if value = null then box "" else
+      if isNull value then box "" else
       match formatMap.TryGetValue(value.GetType()) with
       | true, f -> f value
       | _ -> box (value.ToString())
@@ -404,7 +404,7 @@ type Xl =
          for cf in fs do
             for c in cf.Columns do
                  let colRange = range.Find(c,null,null,Enums.XlLookAt.xlWhole,null)
-                 if colRange <> null then
+                 if not (isNull colRange) then
                      {state with LastRange = (RealExcel  (colRange |> resize(rows,1)))} |> cf.Format |> ignore
          state
 
@@ -415,7 +415,7 @@ type Xl =
          for cf in fs do
             for c in cf.Columns do
                  let colRange = range.Find(c,null,null,Enums.XlLookAt.xlWhole,null)
-                 if colRange <> null then
+                 if not (isNull colRange) then
                      {state with LastRange = (RealExcel  colRange.EntireColumn)} |> cf.Format |> ignore
          state
 
@@ -447,7 +447,7 @@ type Xl =
          let range = (lastRange |> convertRange)
          for cd in ds do
             let colRange = range.Find(cd.Column,null,null,Enums.XlLookAt.xlWhole,null)
-            if colRange <> null then
+            if not (isNull colRange) then
                 let c = colRange.AddComment(cd.Description)
                 c.Visible <- false
                 c.Shape.TextFrame.AutoSize <- true
@@ -459,7 +459,7 @@ type Xl =
          let range = (lastRange |> convertRange)
          let startRange = range.Find(cStart,null,null,Enums.XlLookAt.xlWhole,null)
          let endRange = range.Find(cEnd,null,null,Enums.XlLookAt.xlWhole,null)
-         if startRange <> null && endRange <> null then
+         if not( isNull startRange) && not (isNull endRange) then
              let startAddress = startRange.Address
              let endAddress = endRange.Address
              let r = getRealRange (startAddress + ":" + endAddress)
@@ -528,7 +528,7 @@ type DynamicExcel(app, ?keepInSync) =
         and set (choice) = keepInSync <- choice
 
     member private this.createInstance() =
-        if localExcelApp = null then
+        if isNull localExcelApp then
             localExcelApp <- openNewExcelApplication()
         else
             ()
@@ -644,7 +644,7 @@ let GetFsiSeriesAndFrames (knownTypes : ICollection<Type>) =
                                 && pi.PropertyType <> typeof<Unit>
                                 then
                             let pv = pi.GetValue(null, Array.empty)
-                            if pv <> null then
+                            if not (isNull pv) then
                                 match pv with
                                 | GenericSeries argTypes | GenericFrame argTypes ->
                                     yield { name = pi.Name; type_ = pi.PropertyType; value = pi.GetValue(null, Array.empty); }

src/Deedle/Common/BinomialHeap.fs

@@ -1,4 +1,4 @@
-/// Purely functional Binomial Heap implementation
+/// Purely functional Binomial Heap implementation
 /// Based on: http://cs.hubfs.net/topic/None/56608
 ///
 /// Characteristics:
@@ -40,7 +40,7 @@ module BinomialHeap =
     { Comparer = comparer; Heap = [] }
 
   /// Returns true when the specified heap is emtpy
-  let isEmpty heap = heap.Heap = []
+  let isEmpty heap = List.isEmpty heap.Heap
 
   /// Returns the rank of the specified tree node
   let internal rank (Node (r,_,_)) = r

src/Deedle/Common/Common.fs

@@ -820,7 +820,7 @@ module Seq =
       // Walk over all windows; use 'f' to determine if the item
       // should be added - if so, add it, otherwise yield window
       let win = ref windows.First
-      while win.Value <> null do
+      while not (isNull win.Value) do
         let start, items = win.Value.Value
         let next = win.Value.Next
         if f start v then win.Value.Value <- start, v::items
@@ -1004,7 +1004,7 @@ module Seq =
       // Walk over all windows; use 'f' to determine if the item
       // should be added - if so, add it, otherwise yield window
       let win = ref windows.First
-      while win.Value <> null do
+      while not (isNull win.Value) do
         let value, startIdx, endIdx = win.Value.Value
         let next = win.Value.Next
         if f value v then win.Value.Value <- value, startIdx, !index
@@ -1467,7 +1467,7 @@ module Convert =
         else System.Convert.ChangeType(value, typeof<'T>) :?> 'T
     | ConversionKind.Safe ->
         if value :? 'T then value :?> 'T
-        elif value <> null then
+        elif not (isNull value) then
           match sourcesByTarget.TryGetValue(typeof<'T>) with
           | true, sources when sources.ContainsKey(value.GetType()) ->
               System.Convert.ChangeType(value, typeof<'T>) :?> 'T

src/Deedle/FSharp.Data/CommonRuntime/IO.fs

@@ -1,4 +1,4 @@
-/// Helper functions called from the generated code for working with files
+/// Helper functions called from the generated code for working with files
 module FSharp.Data.Runtime.IO
 
 open System
@@ -7,6 +7,7 @@ open System.IO
 open System.Text
 open FSharp.Data
 
+[<Struct>]
 type internal UriResolutionType =
     | DesignTime
     | Runtime

src/Deedle/FSharp.Data/CommonRuntime/NameUtils.fs

@@ -1,4 +1,4 @@
-/// Tools for generating nice member names that follow F# & .NET naming conventions
+/// Tools for generating nice member names that follow F# & .NET naming conventions
 module FSharp.Data.Runtime.NameUtils
 
 open System
@@ -9,6 +9,7 @@ open FSharp.Data.Runtime
 // --------------------------------------------------------------------------------------
 // Active patterns & operators for parsing strings
 
+// Todo: Convert to ValueTuple and [<return: Struct>] when F# 6 is available
 let private tryAt (s:string) i = if i >= s.Length then None else Some s.[i]
 let private sat f (c:option<char>) = match c with Some c when f c -> Some c | _ -> None
 let private (|EOF|_|) c = match c with Some _ -> None | _ -> Some ()
@@ -18,41 +19,59 @@ let private (|Lower|_|) = sat (fun c -> Char.IsLower c || Char.IsDigit c)
 
 // --------------------------------------------------------------------------------------
 
+let inline internal forall predicate (source : ReadOnlySpan<_>) =
+    let mutable state = true
+    let mutable e = source.GetEnumerator()
+    while state && e.MoveNext() do
+        state <- predicate e.Current
+    state
+
 /// Turns a given non-empty string into a nice 'PascalCase' identifier
 let nicePascalName (s:string) =
   if s.Length = 1 then s.ToUpperInvariant() else
   // Starting to parse a new segment
-  let rec restart i = seq {
+  let rec restart i =
     match tryAt s i with
-    | EOF -> ()
-    | LetterDigit _ & Upper _ -> yield! upperStart i (i + 1)
-    | LetterDigit _ -> yield! consume i false (i + 1)
-    | _ -> yield! restart (i + 1) }
+    | EOF -> Seq.empty
+    | LetterDigit _ & Upper _ -> upperStart i (i + 1)
+    | LetterDigit _ -> consume i false (i + 1)
+    | _ -> restart (i + 1)
   // Parsed first upper case letter, continue either all lower or all upper
-  and upperStart from i = seq {
+  and upperStart from i =
     match tryAt s i with
-    | Upper _ -> yield! consume from true (i + 1)
-    | Lower _ -> yield! consume from false (i + 1)
+    | Upper _ -> consume from true (i + 1)
+    | Lower _ -> consume from false (i + 1)
     | _ ->
-        yield from, i
-        yield! restart (i + 1) }
+        let r1 = struct (from, i)
+        let r2 = restart (i + 1)
+        seq {
+          yield r1
+          yield! r2
+        }
   // Consume are letters of the same kind (either all lower or all upper)
-  and consume from takeUpper i = seq {
-    match tryAt s i with
-    | Lower _ when not takeUpper -> yield! consume from takeUpper (i + 1)
-    | Upper _ when takeUpper -> yield! consume from takeUpper (i + 1)
-    | Lower _ when takeUpper ->
-        yield from, (i - 1)
-        yield! restart (i - 1)
+  and consume from takeUpper i = 
+    match takeUpper, tryAt s i with
+    | false, Lower _ -> consume from takeUpper (i + 1)
+    | true, Upper _ -> consume from takeUpper (i + 1)
+    | true, Lower _ ->
+        let r1 = struct (from, (i - 1))
+        let r2 = restart (i - 1)
+        seq {
+          yield r1
+          yield! r2
+        }
     | _ ->
-        yield from, i
-        yield! restart i }
+        let r1 = struct(from, i)
+        let r2 = restart i
+        seq {
+          yield r1
+          yield! r2 }
 
   // Split string into segments and turn them to PascalCase
   seq { for i1, i2 in restart 0 do
-          let sub = s.Substring(i1, i2 - i1)
-          if Array.forall Char.IsLetterOrDigit (sub.ToCharArray()) then
-            yield sub.[0].ToString().ToUpperInvariant() + sub.ToLowerInvariant().Substring(1) }
+          let sub = s.AsSpan(i1, i2 - i1)
+          if forall Char.IsLetterOrDigit sub then
+            yield Char.ToUpperInvariant(sub.[0]).ToString() + sub.Slice(1).ToString().ToLowerInvariant() }
   |> String.Concat
 
 /// Turns a given non-empty string into a nice 'camelCase' identifier

src/Deedle/FSharp.Data/CommonRuntime/StructuralInference.fs

@@ -303,7 +303,7 @@ let parseUnitOfMeasure (provider:IUnitsOfMeasureProvider) (str:string) =
             if str.EndsWith suffix then
                 let baseUnitStr = str.[..str.Length - suffix.Length - 1]
                 let baseUnit = provider.SI baseUnitStr
-                if baseUnit = null then
+                if isNull baseUnit then
                     None
                 else
                     baseUnit |> trans provider |> Some
@@ -313,4 +313,4 @@ let parseUnitOfMeasure (provider:IUnitsOfMeasureProvider) (str:string) =
     | Some _ -> unit
     | None ->
         let unit = provider.SI str
-        if unit = null then None else Some unit
+        if isNull unit then None else Some unit

src/Deedle/FSharp.Data/CommonRuntime/TextRuntime.fs

@@ -1,4 +1,4 @@
-namespace FSharp.Data.Runtime
+namespace FSharp.Data.Runtime
 
 open System
 open System.Globalization
@@ -19,7 +19,7 @@ type TextRuntime =
     then CultureInfo.InvariantCulture
     else
       let mutable cache = TextRuntime.cultureInfoCache
-      if cache = null then
+      if isNull cache then
         cache                         <- Collections.Generic.Dictionary<string, CultureInfo> ()
         TextRuntime.cultureInfoCache  <- cache
       match cache.TryGetValue cultureStr with

src/Deedle/FSharp.Data/Net/Http.fs

@@ -1199,7 +1199,7 @@ module private HttpHelpers =
             source.Dispose ()
         }
 
-    let runningOnMono = try System.Type.GetType("Mono.Runtime") <> null with e -> false
+    let runningOnMono = try not(isNull (System.Type.GetType "Mono.Runtime")) with e -> false
 
     let writeBody (req:HttpWebRequest) (data: Stream) =
         async {
@@ -1212,7 +1212,7 @@ module private HttpHelpers =
     let reraisePreserveStackTrace (e:Exception) =
         try
             let remoteStackTraceString = typeof<exn>.GetField("_remoteStackTraceString", BindingFlags.Instance ||| BindingFlags.NonPublic);
-            if remoteStackTraceString <> null then
+            if not (isNull remoteStackTraceString) then
                 remoteStackTraceString.SetValue(e, e.StackTrace + Environment.NewLine)
         with _ -> ()
         raise e
@@ -1223,7 +1223,7 @@ module private HttpHelpers =
         with
             // If an exception happens, augment the message with the response
             | :? WebException as exn ->
-              if exn.Response = null then reraisePreserveStackTrace exn
+              if isNull exn.Response then reraisePreserveStackTrace exn
               let responseExn =
                   try
                     let newResponse = new WebResponse(exn.Response)
@@ -1332,7 +1332,7 @@ module private HttpHelpers =
                         return! getResponseAsync req
                     with
                         | :? WebException as exc ->
-                            if exc.Response <> null then
+                            if not (isNull exc.Response) then
                                return exc.Response
                             else
                                 reraisePreserveStackTrace exc
@@ -1601,14 +1601,14 @@ type Http private() =
             let cookies = CookieHandling.getCookiesAndManageCookieContainer uri resp.ResponseUri headers cookieContainer
                                                                             addCookiesFromHeadersToCookieContainer (defaultArg silentCookieErrors false)
 
-            let contentType = if resp.ContentType = null then "application/octet-stream" else resp.ContentType
+            let contentType = if isNull resp.ContentType then "application/octet-stream" else resp.ContentType
 
             let statusCode, characterSet =
                 match resp with
                 | :? HttpWebResponse as resp -> int resp.StatusCode, resp.CharacterSet
                 | _ -> 0, ""
 
-            let characterSet = if characterSet = null then "" else characterSet
+            let characterSet = if isNull characterSet then "" else characterSet
 
             let stream = resp.GetResponseStream()
 

src/Deedle/Frame.fs

@@ -1662,8 +1662,7 @@ and Frame<'TRowKey, 'TColumnKey when 'TRowKey : equality and 'TColumnKey : equal
           |> Seq.zip offsets                                // seq of (srcloc, label)
           |> Seq.zip frame.RowKeys                          // seq of (rowkey, (srcloc, label))
           |> Seq.groupBy (fun (rk, (i, l)) -> l)            // seq of (label, seq of (rowkey, (srcloc, label)))
-          |> Seq.map (fun (k, s) -> s)                      // seq of (seq of (rowkey, (srcloc, label)))
-          |> Seq.concat                                     // seq of (rowkey, (srcloc, label))
+          |> Seq.collect (fun (k, s) -> s)                  // seq of (rowkey, (srcloc, label))
           |> Seq.zip offsets                                // seq of (dstloc, (rowkey, (srcloc, label)))
           |> Seq.map (fun (dst, (rowkey, (src, grp))) ->
              (grp, rowkey), (dst, src))                     // seq of (label, rowkey), (dstloc, srcloc)