Remove List.drop and use List.skip

src/absil/illib.fs

@@ -277,11 +277,6 @@ module List =
         | [] -> None
         | h :: t -> if f h then Some (h, n) else findi (n+1) f t
 
-    let rec drop n l = 
-        match l with 
-        | [] -> []
-        | _ :: xs -> if n=0 then l else drop (n-1) xs
-
     let splitChoose select l =
         let rec ch acc1 acc2 l = 
             match l with 

src/fsharp/ConstraintSolver.fs

@@ -2418,7 +2418,7 @@ and ReportNoCandidatesError (csenv: ConstraintSolverEnv) (nUnnamedCallerArgs, nN
             else
                 if nReqd > nActual then
                     let diff = nReqd - nActual
-                    let missingArgs = List.drop nReqd cmeth.AllUnnamedCalledArgs
+                    let missingArgs = List.skip nReqd cmeth.AllUnnamedCalledArgs
                     match NamesOfCalledArgs missingArgs with 
                     | [] ->
                         if nActual = 0 then 

src/fsharp/DetupleArgs.fs

@@ -465,7 +465,7 @@ let mkTransform g (f: Val) m tps x1Ntys rty (callPattern, tyfringes: (TType list
         | _ -> Some(ValReprInfo (ValReprInfo.InferTyparInfo tps, List.collect ValReprInfoForTS callPattern, ValReprInfo.unnamedRetVal))
     (* type(transformedVal) tyfringes types replace initial arg types of f *)
     let tys1r = List.collect fst tyfringes  (* types for collapsed initial r args *)
-    let tysrN = List.drop tyfringes.Length x1Ntys    (* types for remaining args *)
+    let tysrN = List.skip tyfringes.Length x1Ntys    (* types for remaining args *)
     let argtys = tys1r @ tysrN
     let fCty  = mkLambdaTy tps argtys rty
     let transformedVal =
@@ -784,7 +784,7 @@ let passBind penv (TBind(fOrig, repr, letSeqPtOpt) as bind) =
          let transformedFormals = trans.transformedFormals 
          let p     = transformedFormals.Length
          if (vss.Length < p) then internalError "passBinds: |vss|<p - detuple pass" 
-         let xqNs  = List.drop p vss  
+         let xqNs  = List.skip p vss  
          let x1ps  = List.truncate p vss  
          let y1Ps  = List.concat (List.map2 transFormal transformedFormals x1ps)
          let formals = y1Ps @ xqNs

src/fsharp/FSharp.Core/list.fs

@@ -472,10 +472,11 @@ namespace Microsoft.FSharp.Collections
         let skip count list =
             if count <= 0 then list else
             let rec loop i lst =
+                if i = 0 then lst else
                 match lst with
-                | _ when i = 0 -> lst
                 | _ :: t -> loop (i-1) t
                 | [] -> invalidArgOutOfRange "count" count "distance past the list" i
+
             loop count list
 
         [<CompiledName("SkipWhile")>]

src/fsharp/IlxGen.fs

@@ -5986,7 +5986,7 @@ and GenMethodForBinding
         match v.MemberInfo with
         | Some memberInfo when not v.IsExtensionMember ->
 
-           let ilMethTypars = ilTypars |> List.drop mspec.DeclaringType.GenericArgs.Length
+           let ilMethTypars = ilTypars |> List.skip mspec.DeclaringType.GenericArgs.Length
            if memberInfo.MemberFlags.MemberKind = MemberKind.Constructor then
                assert (isNil ilMethTypars)
                let mdef = mkILCtor (access, ilParams, ilMethodBody)

src/fsharp/NameResolution.fs

@@ -1356,7 +1356,7 @@ let LookupTypeNameInEntityMaybeHaveArity (amap, m, ad, nm, staticResInfo: TypeNa
 /// Handle the .NET/C# business where nested generic types implicitly accumulate the type parameters
 /// from their enclosing types.
 let MakeNestedType (ncenv: NameResolver) (tinst: TType list) m (tcrefNested: TyconRef) =
-    let tps = List.drop tinst.Length (tcrefNested.Typars m)
+    let tps = List.skip tinst.Length (tcrefNested.Typars m)
     let tinstNested = ncenv.InstantiationGenerator m tps
     mkAppTy tcrefNested (tinst @ tinstNested)
 

src/fsharp/TypeChecker.fs

@@ -1628,7 +1628,7 @@ let AdjustAndForgetUsesOfRecValue cenv (vrefTgt: ValRef) (valScheme: ValScheme)
                               errorR(Error(FSComp.SR.tcUnexpectedExprAtRecInfPoint(), m)) 
                               NormalValUse, []
 
-                      let ityargs = generalizeTypars (List.drop (List.length tyargs0) generalizedTypars)
+                      let ityargs = generalizeTypars (List.skip (List.length tyargs0) generalizedTypars)
                       primMkApp (Expr.Val (vrefTgt, vrefFlags, m), fty) (tyargs0 @ ityargs) [] m
                   fixupPoint.Value <- fixedUpExpr)
 
@@ -5070,12 +5070,14 @@ and TcTypeApp cenv newOk checkCxs occ env tpenv m tcref pathTypeArgs (synArgTys:
     // If we're not checking constraints, i.e. when we first assert the super/interfaces of a type definition, then just 
     // clear the constraint lists of the freshly generated type variables. A little ugly but fairly localized. 
     if checkCxs = NoCheckCxs then tps |> List.iter (fun tp -> tp.SetConstraints [])
-    if tinst.Length <> pathTypeArgs.Length + synArgTys.Length then 
-        error (TyconBadArgs(env.DisplayEnv, tcref, pathTypeArgs.Length + synArgTys.Length, m))
+    let synArgTysLength = synArgTys.Length
+    let pathTypeArgsLength = pathTypeArgs.Length
+    if tinst.Length <> pathTypeArgsLength + synArgTysLength then 
+        error (TyconBadArgs(env.DisplayEnv, tcref, pathTypeArgsLength + synArgTysLength, m))
 
     let argTys, tpenv = 
         // Get the suffix of typars
-        let tpsForArgs = List.drop (tps.Length - synArgTys.Length) tps
+        let tpsForArgs = List.skip (tps.Length - synArgTysLength) tps
         let kindsForArgs = tpsForArgs |> List.map (fun tp -> tp.Kind)
         TcTypesOrMeasures (Some kindsForArgs) cenv newOk checkCxs occ env tpenv synArgTys m