List.isEmpty instead of iterating through the list to get the count

src/absil/ilprint.fs

@@ -213,7 +213,7 @@ and goutput_typ_with_shortened_class_syntax env os = function
   | typ2 -> goutput_typ env os typ2
 
 and goutput_gactuals env os inst = 
-  if inst.Length = 0 then () 
+  if List.isEmpty inst then () 
   else  
     output_string os "<";
     output_seq ", " (goutput_gactual env)  os inst
@@ -869,7 +869,7 @@ let goutput_superinterfaces env os imp =
   output_seq "," (goutput_typ_with_shortened_class_syntax env) os imp
 
 let goutput_implements env os (imp:ILTypes) =
-  if imp.Length = 0 then () else
+  if List.isEmpty imp then () else
   output_string os "implements ";
   output_seq "," (goutput_typ_with_shortened_class_syntax env) os imp
 

src/absil/ilread.fs

@@ -1816,7 +1816,7 @@ and seekReadTypeDefOrRef ctxt numtypars boxity (ginst:ILTypes) (TaggedIndex(tag,
     | tag when tag = tdor_TypeDef -> seekReadTypeDefAsType ctxt boxity ginst idx
     | tag when tag = tdor_TypeRef -> seekReadTypeRefAsType ctxt boxity ginst idx
     | tag when tag = tdor_TypeSpec -> 
-        if ginst.Length > 0 then dprintn ("type spec used as type constructor for a generic instantiation: ignoring instantiation")
+        if not (List.isEmpty ginst) then dprintn ("type spec used as type constructor for a generic instantiation: ignoring instantiation")
         readBlobHeapAsType ctxt numtypars (seekReadTypeSpecRow ctxt idx)
     | _ -> failwith "seekReadTypeDefOrRef ctxt"
 

src/absil/ilwrite.fs

@@ -1307,10 +1307,10 @@ and GetMethodDefOrRefAsUncodedToken (tag, idx) =
     getUncodedToken tab idx
 
 and GetMethodSpecInfoAsUncodedToken cenv env ((_, _, _, _, _, _, minst:ILGenericArgs) as minfo) =
-    if minst.Length > 0 then 
-      getUncodedToken TableNames.MethodSpec (GetMethodSpecInfoAsMethodSpecIdx cenv env minfo)
-    else 
-      GetMethodDefOrRefAsUncodedToken (GetMethodRefInfoAsMethodRefOrDef false cenv env (GetMethodRefInfoOfMethodSpecInfo minfo))
+    if List.isEmpty minst then
+        GetMethodDefOrRefAsUncodedToken (GetMethodRefInfoAsMethodRefOrDef false cenv env (GetMethodRefInfoOfMethodSpecInfo minfo))
+    else
+        getUncodedToken TableNames.MethodSpec (GetMethodSpecInfoAsMethodSpecIdx cenv env minfo)
 
 and GetMethodSpecAsUncodedToken cenv env mspec = 
     GetMethodSpecInfoAsUncodedToken cenv env (InfoOfMethodSpec mspec)
@@ -2475,7 +2475,7 @@ let GenReturnPass3 cenv (returnv: ILReturn) =
 let GetMethodDefSigAsBytes cenv env (mdef: ILMethodDef) = 
     emitBytesViaBuffer (fun bb -> 
       bb.EmitByte (callconvToByte mdef.GenericParams.Length mdef.CallingConv)
-      if mdef.GenericParams.Length > 0 then bb.EmitZ32 mdef.GenericParams.Length
+      if not (List.isEmpty mdef.GenericParams) then bb.EmitZ32 mdef.GenericParams.Length
       bb.EmitZ32 mdef.Parameters.Length
       EmitType cenv env bb mdef.Return.Type
       mdef.ParameterTypes |> List.iter (EmitType cenv env bb))

src/fsharp/CompileOps.fs

@@ -4287,7 +4287,7 @@ type TcImports(tcConfigP:TcConfigProvider, initialResolutions:TcAssemblyResoluti
             // specified in the attributes
             |> List.distinctBy (fun s -> try Path.GetFileNameWithoutExtension(s) with _ -> s)
 
-        if designTimeAssemblyNames.Length > 0 then
+        if not (List.isEmpty designTimeAssemblyNames) then
 
             // Find the SystemRuntimeAssemblyVersion value to report in the TypeProviderConfig.
             let primaryAssemblyVersion = 

src/fsharp/IlxGen.fs

@@ -5188,7 +5188,7 @@ and GenMethodForBinding
 
     let permissionSets = CreatePermissionSets cenv.g cenv.amap eenv securityAttributes
 
-    let secDecls = if securityAttributes.Length > 0 then (mkILSecurityDecls permissionSets) else (emptyILSecurityDecls)
+    let secDecls = if List.isEmpty securityAttributes then emptyILSecurityDecls else mkILSecurityDecls permissionSets
 
     // Do not push the attributes to the method for events and properties    
     let ilAttrsCompilerGenerated = if v.IsCompilerGenerated then [  cenv.g.CompilerGeneratedAttribute ] else []
@@ -5207,7 +5207,7 @@ and GenMethodForBinding
         // Does the function have an explicit [<EntryPoint>] attribute? 
         let isExplicitEntryPoint = HasFSharpAttribute cenv.g cenv.g.attrib_EntryPointAttribute attrs
 
-        let mdef = mdef.WithSecurity(securityAttributes.Length > 0).WithPInvoke(hasDllImport)
+        let mdef = mdef.WithSecurity(not (List.isEmpty securityAttributes)).WithPInvoke(hasDllImport)
         let mdef = mdef.WithPreserveSig(hasPreserveSigImplFlag || hasPreserveSigNamedArg).WithSynchronized(hasSynchronizedImplFlag).WithNoInlining(hasNoInliningFlag).WithAggressiveInlining(hasAggressiveInliningImplFlag)
         let mdef =
             { mdef with 
@@ -6238,7 +6238,7 @@ and GenTypeDef cenv mgbuf lazyInitInfo eenv m (tycon:Tycon) =
                                     not (HasFSharpAttribute cenv.g cenv.g.attrib_DebuggerTypeProxyAttribute tycon.Attribs))
 
         let permissionSets = CreatePermissionSets cenv.g cenv.amap eenv securityAttrs
-        let secDecls = if securityAttrs.Length > 0 then (mkILSecurityDecls permissionSets) else (emptyILSecurityDecls)
+        let secDecls = if List.isEmpty securityAttrs then emptyILSecurityDecls else mkILSecurityDecls permissionSets
 
         let ilDebugDisplayAttributes = 
             [ yield! GenAttrs cenv eenv debugDisplayAttrs
@@ -6699,7 +6699,7 @@ and GenTypeDef cenv mgbuf lazyInitInfo eenv m (tycon:Tycon) =
 
            | _ -> failwith "??"
 
-        let tdef = tdef.WithHasSecurity(securityAttrs.Length > 0)
+        let tdef = tdef.WithHasSecurity(not (List.isEmpty securityAttrs))
         let tdef = 
             { tdef with 
                 SecurityDecls = secDecls }

src/fsharp/LexFilter.fs

@@ -444,7 +444,7 @@ type TokenTup =
 let (|TyparsCloseOp|_|) (txt:string) = 
     let angles = txt |> Seq.takeWhile (fun c -> c = '>') |> Seq.toList
     let afterAngles = txt |> Seq.skipWhile (fun c -> c = '>') |> Seq.toList
-    if angles.Length = 0 then None else
+    if List.isEmpty angles then None else
 
     let afterOp = 
         match (new System.String(Array.ofSeq afterAngles)) with 

src/fsharp/MethodOverrides.fs

@@ -709,7 +709,7 @@ let GetAbstractMethInfosForSynMethodDecl(infoReader:InfoReader,ad,memberName:Ide
             GetIntrinsicMethInfosOfType infoReader (Some(memberName.idText), ad, AllowMultiIntfInstantiations.Yes) IgnoreOverrides bindm ty
     let dispatchSlots = minfos |> List.filter (fun minfo -> minfo.IsDispatchSlot)
     let topValSynArities = SynInfo.AritiesOfArgs valSynData
-    let topValSynArities = if topValSynArities.Length > 0 then topValSynArities.Tail else topValSynArities
+    let topValSynArities = if List.isEmpty topValSynArities then topValSynArities else topValSynArities.Tail
     let dispatchSlotsArityMatch = dispatchSlots |> List.filter (fun minfo -> minfo.NumArgs = topValSynArities) 
     dispatchSlots,dispatchSlotsArityMatch 
 

src/fsharp/NameResolution.fs

@@ -568,7 +568,7 @@ let AddValRefToNameEnv nenv (vref:ValRef) =
 
 /// Add a set of active pattern result tags to the environment.
 let AddActivePatternResultTagsToNameEnv (apinfo: PrettyNaming.ActivePatternInfo) nenv ty m =
-    if apinfo.Names.Length = 0 then nenv else
+    if List.isEmpty apinfo.Names then nenv else
     let apresl = List.indexed apinfo.Names
     { nenv with
         eUnqualifiedItems = 
@@ -675,13 +675,13 @@ let private AddPartsOfTyconRefToNameEnv bulkAddMode ownDefinition (g:TcGlobals)
                     | _ -> Item.UnqualifiedType [tcref]))
             else
                 tab
-        if isILOrRequiredQualifiedAccess || ucrefs.Length = 0 then 
+        if isILOrRequiredQualifiedAccess || List.isEmpty ucrefs then 
             tab 
         else 
             AddUnionCases2 bulkAddMode tab ucrefs
 
     let ePatItems = 
-        if isILOrRequiredQualifiedAccess || ucrefs.Length = 0 then 
+        if isILOrRequiredQualifiedAccess || List.isEmpty ucrefs then 
             nenv.ePatItems 
         else 
             AddUnionCases1 nenv.ePatItems ucrefs
@@ -1725,14 +1725,14 @@ let CheckForTypeLegitimacyAndMultipleGenericTypeAmbiguities
                 // no explicit type instantiation
                 typeNameResInfo.StaticArgsInfo.HasNoStaticArgsInfo && 
                 // some type arguments required on all types (note sorted by typar count above)
-                tcref.Typars(m).Length > 0 && 
+                not (List.isEmpty (tcref.Typars m)) && 
                 // plausible types have different arities
                 (tcrefs |> Seq.distinctBy (fun (_,tcref) -> tcref.Typars(m).Length) |> Seq.length > 1)  ->
             [ for (resInfo,tcref) in tcrefs do 
                 let resInfo = resInfo.AddWarning (fun _typarChecker -> errorR(Error(FSComp.SR.nrTypeInstantiationNeededToDisambiguateTypesWithSameName(tcref.DisplayName, tcref.DisplayNameWithStaticParametersAndUnderscoreTypars),m)))
                 yield (resInfo,tcref) ]
 
-        | [(resInfo,tcref)] when  typeNameResInfo.StaticArgsInfo.HasNoStaticArgsInfo && tcref.Typars(m).Length > 0 && typeNameResInfo.ResolutionFlag = ResolveTypeNamesToTypeRefs ->
+        | [(resInfo,tcref)] when  typeNameResInfo.StaticArgsInfo.HasNoStaticArgsInfo && not (List.isEmpty (tcref.Typars m)) && typeNameResInfo.ResolutionFlag = ResolveTypeNamesToTypeRefs ->
             let resInfo = 
                 resInfo.AddWarning (fun (ResultTyparChecker typarChecker) -> 
                     if not (typarChecker()) then 
@@ -3223,9 +3223,9 @@ let NeedsWorkAfterResolution namedItem =
     | Item.CtorGroup(_,minfos) -> minfos.Length > 1 || minfos |> List.exists (fun minfo -> not (isNil minfo.FormalMethodInst))
     | Item.Property(_,pinfos) -> pinfos.Length > 1
     | Item.ImplicitOp(_, { contents = Some(TraitConstraintSln.FSMethSln(_, vref, _)) }) 
-    | Item.Value vref | Item.CustomBuilder (_,vref) -> vref.Typars.Length > 0
+    | Item.Value vref | Item.CustomBuilder (_,vref) -> not (List.isEmpty vref.Typars)
     | Item.CustomOperation (_,_,Some minfo) -> not (isNil minfo.FormalMethodInst)
-    | Item.ActivePatternCase apref -> apref.ActivePatternVal.Typars.Length > 0
+    | Item.ActivePatternCase apref -> not (List.isEmpty apref.ActivePatternVal.Typars)
     | _ -> false
 
 /// Specifies additional work to do after an item has been processed further in type checking.

src/fsharp/Optimizer.fs

@@ -2507,7 +2507,7 @@ and TryInlineApplication cenv env finfo (tyargs: TType list, args: Expr list, m)
               false
             else true)))) ->
 
-        let isBaseCall =  args.Length > 0 &&          
+        let isBaseCall = not (List.isEmpty args) &&
                               match args.[0] with
                               | Expr.Val(vref, _, _) when vref.BaseOrThisInfo = BaseVal -> true
                               | _ -> false

src/fsharp/TypeChecker.fs

@@ -2810,7 +2810,7 @@ let TcVal checkAttributes cenv env tpenv (vref:ValRef) optInst optAfterResolutio
                       // If we have got an explicit instantiation then use that 
                       | Some(vrefFlags, checkTys) -> 
                             let checkInst (tinst:TypeInst) = 
-                                if not v.IsMember && not v.PermitsExplicitTypeInstantiation && tinst.Length > 0 && v.Typars.Length > 0 then 
+                                if not v.IsMember && not v.PermitsExplicitTypeInstantiation && not (List.isEmpty tinst) && not (List.isEmpty v.Typars) then 
                                     warning(Error(FSComp.SR.tcDoesNotAllowExplicitTypeArguments(v.DisplayName), m))
                             match vrec with 
                             | ValInRecScope false -> 
@@ -7493,13 +7493,13 @@ and TcComputationExpression cenv env overallTy mWhole interpExpr builderTy tpenv
         | StripApps(SingleIdent nm, [StripApps(SingleIdent nm2, args); arg2]) when 
                   PrettyNaming.IsInfixOperator nm.idText && 
                   expectedArgCountForCustomOperator nm2 > 0 &&
-                  args.Length > 0 -> 
+                  not (List.isEmpty args) -> 
             let estimatedRangeOfIntendedLeftAndRightArguments = unionRanges (List.last args).Range arg2.Range
             errorR(Error(FSComp.SR.tcUnrecognizedQueryBinaryOperator(), estimatedRangeOfIntendedLeftAndRightArguments))
             true
         | SynExpr.Tuple( (StripApps(SingleIdent nm2, args) :: _), _, m) when 
                   expectedArgCountForCustomOperator nm2 > 0 &&
-                  args.Length > 0 -> 
+                  not (List.isEmpty args) -> 
             let estimatedRangeOfIntendedLeftAndRightArguments = unionRanges (List.last args).Range m.EndRange
             errorR(Error(FSComp.SR.tcUnrecognizedQueryBinaryOperator(), estimatedRangeOfIntendedLeftAndRightArguments))
             true
@@ -11252,7 +11252,7 @@ and AnalyzeAndMakeAndPublishRecursiveValue overridesOK isGeneratedEventVal cenv
     let prelimTyscheme = TypeScheme(enclosingDeclaredTypars@declaredTypars, ty)
     let partialValReprInfo = TranslateTopValSynInfo mBinding (TcAttributes cenv envinner) valSynInfo
     let topValInfo = UseSyntacticArity declKind prelimTyscheme partialValReprInfo
-    let hasDeclaredTypars = declaredTypars.Length > 0
+    let hasDeclaredTypars = not (List.isEmpty declaredTypars)
     let prelimValScheme = ValScheme(bindingId, prelimTyscheme, topValInfo, memberInfoOpt, false, inlineFlag, NormalVal, vis, false, false, false, hasDeclaredTypars)
 
     // Check the literal r.h.s., if any
@@ -13574,14 +13574,14 @@ module MutRecBindingChecking =
         let ad = env.eAccessRights
         let mvvs = ForceRaise (ResolveLongIndentAsModuleOrNamespace cenv.tcSink ResultCollectionSettings.AllResults cenv.amap m OpenQualified env.eNameResEnv ad p false)
         let modrefs = mvvs |> List.map p23 
-        if modrefs.Length > 0 && modrefs |> List.forall (fun modref -> modref.IsNamespace) then 
+        if not (List.isEmpty modrefs) && modrefs |> List.forall (fun modref -> modref.IsNamespace) then 
             errorR(Error(FSComp.SR.tcModuleAbbreviationForNamespace(fullDisplayTextOfModRef (List.head modrefs)), m))
         let modrefs = modrefs |> List.filter (fun mvv -> not mvv.IsNamespace)
+        if List.isEmpty modrefs then env else 
         modrefs |> List.iter (fun modref -> CheckEntityAttributes cenv.g modref m |> CommitOperationResult)        
-        let env = (if modrefs.Length > 0 then AddModuleAbbreviationAndReport cenv.tcSink scopem id modrefs env else env)
+        let env = AddModuleAbbreviationAndReport cenv.tcSink scopem id modrefs env
         env
 
-
     /// Update the contents accessible via the recursive namespace declaration, if any
     let TcMutRecDefns_UpdateNSContents mutRecNSInfo =
         match mutRecNSInfo with 
@@ -15128,10 +15128,10 @@ module EstablishTypeDefinitionCores =
                     if allowed then 
                         if kind = explicitKind then
                             warning(PossibleUnverifiableCode(m))
-                    elif thisTyconRef.Typars(m).Length > 0 then 
-                        errorR (Error(FSComp.SR.tcGenericTypesCannotHaveStructLayout(), m))
-                    else
+                    elif List.isEmpty (thisTyconRef.Typars m) then
                         errorR (Error(FSComp.SR.tcOnlyStructsCanHaveStructLayout(), m))
+                    else
+                        errorR (Error(FSComp.SR.tcGenericTypesCannotHaveStructLayout(), m))
                 | None -> ()
 
             let hiddenReprChecks(hasRepr) =
@@ -16361,14 +16361,13 @@ let rec TcSignatureElementNonMutRec cenv parent typeNames endm (env: TcEnv) synS
 
             let modrefs = unfilteredModrefs |> List.filter (fun modref -> not modref.IsNamespace)
 
-            if unfilteredModrefs.Length > 0 && List.isEmpty modrefs then 
+            if not (List.isEmpty unfilteredModrefs) && List.isEmpty modrefs then 
                 errorR(Error(FSComp.SR.tcModuleAbbreviationForNamespace(fullDisplayTextOfModRef (List.head unfilteredModrefs)), m))
 
+            if List.isEmpty modrefs then return env else
             modrefs |> List.iter (fun modref -> CheckEntityAttributes cenv.g modref m |> CommitOperationResult)        
 
-            let env = 
-                if modrefs.Length > 0 then AddModuleAbbreviationAndReport cenv.tcSink scopem id modrefs env 
-                else env
+            let env = AddModuleAbbreviationAndReport cenv.tcSink scopem id modrefs env 
             return env
 
         | SynModuleSigDecl.HashDirective _ -> 

src/fsharp/fsc.fs

@@ -1966,7 +1966,7 @@ let main2b (tcImportsCapture,dynamicAssemblyCreator) (Args (ctok, tcConfig: TcCo
     // remove any security attributes from the top-level assembly attribute list
     let topAttrs = {topAttrs with assemblyAttrs=topAssemblyAttrs}
     let permissionSets = ilxGenerator.CreatePermissionSets securityAttrs
-    let secDecls = if securityAttrs.Length > 0 then mkILSecurityDecls permissionSets else emptyILSecurityDecls
+    let secDecls = if List.isEmpty securityAttrs then emptyILSecurityDecls else mkILSecurityDecls permissionSets
 
     let ilxMainModule = MainModuleBuilder.CreateMainModule (ctok, tcConfig, tcGlobals, tcImports, pdbfile, assemblyName, outfile, topAttrs, idata, optDataResources, codegenResults, assemVerFromAttrib, metadataVersion, secDecls)
 

src/fsharp/fsi/fsi.fs

@@ -2029,7 +2029,7 @@ type internal FsiInteractionProcessor
 
                 // When the last declaration has a shape of DoExp (i.e., non-binding), 
                 // transform it to a shape of "let it = <exp>", so we can refer it.
-                let defsA = if defsA.Length <= 1 || defsB.Length > 0 then  defsA else
+                let defsA = if defsA.Length <= 1 || not (List.isEmpty defsB) then defsA else
                             match List.headAndTail (List.rev defsA) with
                             | SynModuleDecl.DoExpr(_,exp,_), rest -> (rest |> List.rev) @ (fsiDynamicCompiler.BuildItBinding exp)
                             | _ -> defsA

src/fsharp/tast.fs

@@ -604,7 +604,7 @@ type Entity =
             | [] -> nm
             | tps -> 
                 let nm = DemangleGenericTypeName nm
-                if withUnderscoreTypars && tps.Length > 0 then 
+                if withUnderscoreTypars && not (List.isEmpty tps) then 
                     nm + "<" + String.concat "," (Array.create tps.Length "_") + ">"
                 else
                     nm