Generics support

ConsumePlugin/Catamorphism.fs

@@ -11,12 +11,12 @@ type PairOpKind =
     | ThenDoSeq
 
 [<CreateCatamorphism "TreeCata">]
-type Tree<'a> =
-    | Const of Const<'a>
-    | Pair of Tree<'a> * Tree<'a> * PairOpKind
-    | Sequential of Tree<'a> list
-    | Builder of Tree<'a> * TreeBuilder<'a>
+type Tree<'a, 'b> =
+    | Const of Const<'a> * 'b
+    | Pair of Tree<'a, 'b> * Tree<'a, 'b> * PairOpKind
+    | Sequential of Tree<'a, 'b> list
+    | Builder of Tree<'a, 'b> * TreeBuilder<'b, 'a>
 
-and TreeBuilder<'a> =
-    | Child of TreeBuilder<'a>
-    | Parent of Tree<'a>
+and TreeBuilder<'b, 'a> =
+    | Child of TreeBuilder<'b, 'a>
+    | Parent of Tree<'a, 'b>

ConsumePlugin/GeneratedCatamorphism.fs

@@ -12,16 +12,16 @@ namespace ConsumePlugin
 open WoofWare.Myriad.Plugins
 
 /// Description of how to combine cases during a fold
-type TreeBuilderCataCase<'a, 'TreeBuilder, 'Tree> =
+type TreeBuilderCataCase<'b, 'a, 'TreeBuilder, 'Tree> =
     /// How to operate on the Child case
     abstract Child : 'TreeBuilder -> 'TreeBuilder
     /// How to operate on the Parent case
     abstract Parent : 'Tree -> 'TreeBuilder
 
 /// Description of how to combine cases during a fold
-type TreeCataCase<'a, 'TreeBuilder, 'Tree> =
+type TreeCataCase<'a, 'b, 'TreeBuilder, 'Tree> =
     /// How to operate on the Const case
-    abstract Const : Const -> 'Tree
+    abstract Const : Const<'a> -> 'b -> 'Tree
     /// How to operate on the Pair case
     abstract Pair : 'Tree -> 'Tree -> PairOpKind -> 'Tree
     /// How to operate on the Sequential case
@@ -30,30 +30,30 @@ type TreeCataCase<'a, 'TreeBuilder, 'Tree> =
     abstract Builder : 'Tree -> 'TreeBuilder -> 'Tree
 
 /// Specifies how to perform a fold (catamorphism) over the type Tree and its friends.
-type TreeCata<'a, 'a, 'TreeBuilder, 'Tree> =
+type TreeCata<'b, 'a, 'TreeBuilder, 'Tree> =
     {
         /// How to perform a fold (catamorphism) over the type TreeBuilder
-        TreeBuilder : TreeBuilderCataCase<'a, 'TreeBuilder, 'Tree>
+        TreeBuilder : TreeBuilderCataCase<'b, 'a, 'TreeBuilder, 'Tree>
         /// How to perform a fold (catamorphism) over the type Tree
-        Tree : TreeCataCase<'a, 'TreeBuilder, 'Tree>
+        Tree : TreeCataCase<'a, 'b, 'TreeBuilder, 'Tree>
     }
 
 /// Methods to perform a catamorphism over the type Tree
 [<RequireQualifiedAccess>]
 module TreeCata =
     [<RequireQualifiedAccess>]
-    type private Instruction<'a, 'a> =
-        | Process__TreeBuilder of TreeBuilder<'a>
-        | Process__Tree of Tree<'a>
+    type private Instruction<'b, 'a> =
+        | Process__TreeBuilder of TreeBuilder<'b, 'a>
+        | Process__Tree of Tree<'a, 'b>
         | TreeBuilder_Child
         | TreeBuilder_Parent
         | Tree_Pair of PairOpKind
         | Tree_Sequential of int
         | Tree_Builder
 
-    let private loop (cata : TreeCata<_, _, _, _>) (instructions : ResizeArray<Instruction<_, _>>) =
-        let treeStack = ResizeArray ()
-        let treeBuilderStack = ResizeArray ()
+    let private loop (cata : TreeCata<'b, 'a, 'TreeBuilder, 'Tree>) (instructions : ResizeArray<Instruction<'b, 'a>>) =
+        let treeStack = ResizeArray<'Tree> ()
+        let treeBuilderStack = ResizeArray<'TreeBuilder> ()
 
         while instructions.Count > 0 do
             let currentInstruction = instructions.[instructions.Count - 1]
@@ -70,7 +70,7 @@ module TreeCata =
                     instructions.Add (Instruction.Process__Tree arg0_0)
             | Instruction.Process__Tree x ->
                 match x with
-                | Tree.Const (arg0_0) -> cata.Tree.Const arg0_0 |> treeStack.Add
+                | Tree.Const (arg0_0, arg1_0) -> cata.Tree.Const arg0_0 arg1_0 |> treeStack.Add
                 | Tree.Pair (arg0_0, arg1_0, arg2_0) ->
                     instructions.Add (Instruction.Tree_Pair (arg2_0))
                     instructions.Add (Instruction.Process__Tree arg0_0)
@@ -121,8 +121,8 @@ module TreeCata =
 
     /// Execute the catamorphism.
     let runTreeBuilder
-        (cata : TreeCata<'a, 'a, 'TreeBuilderRet, 'TreeRet>)
-        (x : TreeBuilder<'a, 'a>)
+        (cata : TreeCata<'b, 'a, 'TreeBuilderRet, 'TreeRet>)
+        (x : TreeBuilder<'b, 'a>)
         : 'TreeBuilderRet
         =
         let instructions = ResizeArray ()
@@ -131,7 +131,7 @@ module TreeCata =
         Seq.exactlyOne treeBuilderRetStack
 
     /// Execute the catamorphism.
-    let runTree (cata : TreeCata<'a, 'a, 'TreeBuilderRet, 'TreeRet>) (x : Tree<'a, 'a>) : 'TreeRet =
+    let runTree (cata : TreeCata<'b, 'a, 'TreeBuilderRet, 'TreeRet>) (x : Tree<'a, 'b>) : 'TreeRet =
         let instructions = ResizeArray ()
         instructions.Add (Instruction.Process__Tree x)
         let treeBuilderRetStack, treeRetStack = loop cata instructions

ConsumePlugin/GeneratedFileSystem.fs

@@ -33,8 +33,8 @@ module FileSystemItemCata =
         | Process__FileSystemItem of FileSystemItem
         | FileSystemItem_Directory of string * int * int
 
-    let private loop (cata : FileSystemCata<_>) (instructions : ResizeArray<Instruction>) =
-        let fileSystemItemStack = ResizeArray ()
+    let private loop (cata : FileSystemCata<'FileSystemItem>) (instructions : ResizeArray<Instruction>) =
+        let fileSystemItemStack = ResizeArray<'FileSystemItem> ()
 
         while instructions.Count > 0 do
             let currentInstruction = instructions.[instructions.Count - 1]
@@ -108,8 +108,8 @@ module GiftCata =
         | Gift_Boxed
         | Gift_WithACard of string
 
-    let private loop (cata : GiftCata<_>) (instructions : ResizeArray<Instruction>) =
-        let giftStack = ResizeArray ()
+    let private loop (cata : GiftCata<'Gift>) (instructions : ResizeArray<Instruction>) =
+        let giftStack = ResizeArray<'Gift> ()
 
         while instructions.Count > 0 do
             let currentInstruction = instructions.[instructions.Count - 1]

ConsumePlugin/ListCata.fs

@@ -33,8 +33,8 @@ module MyListCata =
         | Process__MyList of MyList<'a>
         | MyList_Cons of 'a
 
-    let private loop (cata : MyListCata<_, _>) (instructions : ResizeArray<Instruction<_>>) =
-        let myListStack = ResizeArray ()
+    let private loop (cata : MyListCata<'a, 'MyList>) (instructions : ResizeArray<Instruction<'a>>) =
+        let myListStack = ResizeArray<'MyList> ()
 
         while instructions.Count > 0 do
             let currentInstruction = instructions.[instructions.Count - 1]
@@ -89,8 +89,8 @@ module MyList2Cata =
         | Process__MyList2 of MyList2<'a>
         | MyList2_Cons of 'a
 
-    let private loop (cata : MyList2Cata<_, _>) (instructions : ResizeArray<Instruction<_>>) =
-        let myList2Stack = ResizeArray ()
+    let private loop (cata : MyList2Cata<'a, 'MyList2>) (instructions : ResizeArray<Instruction<'a>>) =
+        let myList2Stack = ResizeArray<'MyList2> ()
 
         while instructions.Count > 0 do
             let currentInstruction = instructions.[instructions.Count - 1]

README.md

@@ -332,7 +332,7 @@ thereby allowing the programmer to use F#'s record-update syntax.
 Takes a collection of mutually recursive discriminated unions:
 
 ```fsharp
-[<CreateCatamorphism>]
+[<CreateCatamorphism "MyCata">]
 type Expr =
     | Const of Const
     | Pair of Expr * Expr * PairOpKind
@@ -356,7 +356,7 @@ type ExprBuilderCata<'Expr, 'ExprBuilder> =
     abstract Child : 'ExprBuilder -> 'ExprBuilder
     abstract Parent : 'Expr -> 'ExprBuilder
 
-type Cata<'Expr, 'ExprBuilder> =
+type MyCata<'Expr, 'ExprBuilder> =
     {
         Expr : ExprCata<'Expr, 'ExprBuilder>
         ExprBuilder : ExprBuilderCata<'Expr, 'ExprBuilder>
@@ -364,10 +364,10 @@ type Cata<'Expr, 'ExprBuilder> =
 
 [<RequireQualifiedAccess>]
 module ExprCata =
-    let runExpr (cata : Cata<'ExprRet, 'ExprBuilderRet>) (x : Expr) : 'ExprRet =
+    let runExpr (cata : MyCata<'ExprRet, 'ExprBuilderRet>) (x : Expr) : 'ExprRet =
         failwith "this is implemented"
 
-    let runExprBuilder (cata : Cata<'ExprRet, 'ExprBuilderRet>) (x : ExprBuilder) : 'ExprBuilderRet =
+    let runExprBuilder (cata : MyCata<'ExprRet, 'ExprBuilderRet>) (x : ExprBuilder) : 'ExprBuilderRet =
         failwith "this is implemented"
 ```
 
@@ -381,6 +381,10 @@ and then each time you only plug in what you want to do.
 * Mutually recursive DUs are supported (as in the example above).
   Every DU in a recursive `type Foo... and Bar...` knot will be given an appropriate cata, as long as any one of those DUs has the `[<CreateCatamorphism>]` attribute.
 * There is *limited* support for records and for lists.
+* There is *extremely brittle* support for generics in the DUs you are cata'ing over.
+  It is based on the names of the generic parameters, so you must ensure that generic parameters with the same name have the same meaning across the various cases in your recursive knot of DUs.
+  (If you overstep the bounds of what this generator can do, you will get compile-time errors, e.g. with generics being constrained to each other's values.)
+  See the [List tests](./WoofWare.Myriad.Plugins.Test/TestCataGenerator/TestMyList2.fs) for an example, where we re-implement `FSharpList<'a>`.
 
 ### Limitations
 

WoofWare.Myriad.Plugins.Test/TestCataGenerator/TestCataGenerator.fs

@@ -8,17 +8,17 @@ open FsCheck
 
 [<TestFixture>]
 module TestCataGenerator =
-    let idCata : TreeCata<_, _> =
+    let idCata<'a, 'b> : TreeCata<'a, 'b, _, _> =
         {
             Tree =
-                { new TreeCataCase<_, _> with
-                    member _.Const x = Const x
+                { new TreeCataCase<_, _, _, _> with
+                    member _.Const x y = Const (x, y)
                     member _.Pair x y z = Pair (x, y, z)
                     member _.Sequential xs = Sequential xs
                     member _.Builder x b = Builder (x, b)
                 }
             TreeBuilder =
-                { new TreeBuilderCataCase<_, _> with
+                { new TreeBuilderCataCase<_, _, _, _> with
                     member _.Child x = Child x
                     member _.Parent x = Parent x
                 }
@@ -27,7 +27,7 @@ module TestCataGenerator =
     [<Test>]
     let ``Example`` () =
         let x =
-            Tree.Pair (Tree.Const (Const.Int 0), Tree.Const (Const.String ""), PairOpKind.ThenDoSeq)
+            Tree.Pair (Tree.Const (Const.Verbatim 0, "hi"), Tree.Const (Const.String "", "bye"), PairOpKind.ThenDoSeq)
 
         TreeCata.runTree idCata x |> shouldEqual x
 
@@ -36,7 +36,7 @@ module TestCataGenerator =
     let ``Cata works`` () =
         let builderCases = ref 0
 
-        let property (x : Tree) =
+        let property (x : Tree<int, string>) =
             match x with
             | Tree.Builder _ -> Interlocked.Increment builderCases |> ignore
             | _ -> ()

WoofWare.Myriad.Plugins.Test/TestCataGenerator/TestMyList.fs

@@ -21,7 +21,6 @@ module TestMyList =
                                 Tail = tail
                             }
                 }
-
         }
 
     [<Test>]

WoofWare.Myriad.Plugins.Test/TestCataGenerator/TestMyList2.fs

@@ -14,9 +14,8 @@ module TestMyList2 =
                 { new MyList2CataCase<'a, _> with
                     member _.Nil = MyList2.Nil
 
-                    member _.Cons head tail = MyList2.Cons (head, tail)
+                    member _.Cons (head : 'a) (tail : MyList2<'a>) = MyList2.Cons (head, tail)
                 }
-
         }
 
     [<Test>]

WoofWare.Myriad.Plugins/AstHelper.fs

@@ -76,6 +76,9 @@ type internal AdtNode =
     {
         Type : SynType
         Name : Ident option
+        /// An ordered list, so you can look up any given generic within `this.Type`
+        /// to discover what its index is in the parent DU which defined it.
+        GenericsOfParent : SynTyparDecl list
     }
 
 /// A DU is a sum of products (e.g. `type Thing = Foo of a * b`);
@@ -85,6 +88,10 @@ type internal AdtProduct =
     {
         Name : SynIdent
         Fields : AdtNode list
+        /// This AdtProduct represents a product in which there might be
+        /// some bound type parameters. This field lists the bound
+        /// type parameters in the order they appeared on the parent type.
+        Generics : SynTyparDecl list
     }
 
 [<RequireQualifiedAccess>]
@@ -435,15 +442,30 @@ module internal AstHelper =
                                     {
                                         Type = ty
                                         Name = id
+                                        GenericsOfParent = typars
                                     }
                                 )
+                            Generics = typars
                         }
                 )
 
             cases, typars, access
         | _ -> failwithf "Failed to get union cases for type that was: %+A" repr
 
-    let getRecordFields (SynTypeDefn.SynTypeDefn (_, repr, _, _, _, _)) : AdtNode list =
+    let getRecordFields (SynTypeDefn.SynTypeDefn (typeInfo, repr, _, _, _, _)) : AdtNode list =
+        let (SynComponentInfo.SynComponentInfo (typeParams = typars)) = typeInfo
+
+        let typars =
+            match typars with
+            | None -> []
+            | Some (SynTyparDecls.PrefixList (decls, _)) -> decls
+            | Some (SynTyparDecls.SinglePrefix (l, _)) -> [ l ]
+            | Some (SynTyparDecls.PostfixList (decls, constraints, _)) ->
+                if not constraints.IsEmpty then
+                    failwith "Constrained type parameters not currently supported"
+
+                decls
+
         match repr with
         | SynTypeDefnRepr.Simple (SynTypeDefnSimpleRepr.Record (_, fields, _), _) ->
             fields
@@ -451,6 +473,7 @@ module internal AstHelper =
                 {
                     Name = ident
                     Type = ty
+                    GenericsOfParent = typars
                 }
             )
         | _ -> failwithf "Failed to get record elements for type that was: %+A" repr

WoofWare.Myriad.Plugins/CataGenerator.fs

@@ -35,8 +35,10 @@ module internal CataGenerator =
             /// The relationship this field has with the parent type (or the
             /// recursive knot of parent types)
             Description : FieldDescription
-            /// Any generic parameters this field consumes
-            RequiredGenerics : SynType list option
+            /// Any generic parameters this field consumes.
+            /// This only makes sense in the context of a UnionAnalysis:
+            /// it is an index into the parent Union's collection of generic parameters.
+            RequiredGenerics : int list option
         }
 
     type CataUnionRecordField = (Ident * CataUnionBasicField) list
@@ -119,12 +121,10 @@ module internal CataGenerator =
         (userProvidedTypars : SynTyparDecl list)
         (allArtificialTypars : SynType list)
         (relevantTypar : SynType)
-        (unionType : SynTypeDefn)
+        (analysis : UnionAnalysis)
         : SynBinding
         =
-        let relevantTypeName =
-            match unionType with
-            | SynTypeDefn.SynTypeDefn (SynComponentInfo.SynComponentInfo (longId = id), _, _, _, _, _) -> List.last id
+        let relevantTypeName = analysis.ParentTypeName
 
         let allArtificialTyparNames =
             allArtificialTypars
@@ -134,7 +134,11 @@ module internal CataGenerator =
                 | _ -> failwith "logic error in generator"
             )
 
-        let userProvidedTypars =
+        let userProvidedTyparsForCase =
+            analysis.Typars
+            |> List.map (fun (SynTyparDecl.SynTyparDecl (_, ty)) -> SynType.Var (ty, range0))
+
+        let userProvidedTyparsForCata =
             userProvidedTypars
             |> List.map (fun (SynTyparDecl.SynTyparDecl (_, ty)) -> SynType.Var (ty, range0))
 
@@ -145,7 +149,7 @@ module internal CataGenerator =
 
         let inputObjectType =
             let baseType =
-                SynType.CreateLongIdent (SynLongIdent.CreateFromLongIdent [ relevantTypeName ])
+                SynType.CreateLongIdent (SynLongIdent.CreateFromLongIdent relevantTypeName)
 
             if userProvidedTypars.Length = 0 then
                 baseType
@@ -153,7 +157,7 @@ module internal CataGenerator =
                 SynType.App (
                     baseType,
                     Some range0,
-                    userProvidedTypars,
+                    userProvidedTyparsForCase,
                     List.replicate (userProvidedTypars.Length - 1) range0,
                     Some range0,
                     false,
@@ -170,7 +174,7 @@ module internal CataGenerator =
                 SynType.App (
                     SynType.CreateLongIdent (SynLongIdent.CreateFromLongIdent [ cataName ]),
                     Some range0,
-                    userProvidedTypars @ allArtificialTypars,
+                    userProvidedTyparsForCata @ allArtificialTypars,
                     List.replicate (userProvidedTypars.Length + allArtificialTypars.Length - 1) range0,
                     Some range0,
                     false,
@@ -194,8 +198,8 @@ module internal CataGenerator =
                 None
             ),
             SynPat.CreateLongIdent (
-                SynLongIdent.CreateString ("run" + relevantTypeName.idText),
-                [ SynPat.CreateParen (cataObject) ; SynPat.CreateParen inputObject ]
+                SynLongIdent.CreateString ("run" + List.last(relevantTypeName).idText),
+                [ SynPat.CreateParen cataObject ; SynPat.CreateParen inputObject ]
             ),
             Some (SynBindingReturnInfo.Create relevantTypar),
             SynExpr.CreateTyped (
@@ -219,10 +223,7 @@ module internal CataGenerator =
                                 SynExpr.CreateLongIdent (SynLongIdent.Create [ "instructions" ; "Add" ]),
                                 SynExpr.CreateParen (
                                     SynExpr.CreateApp (
-                                        SynExpr.CreateLongIdent (
-                                            SynLongIdent.Create
-                                                [ "Instruction" ; "Process__" + relevantTypeName.idText ]
-                                        ),
+                                        SynExpr.CreateLongIdent analysis.AssociatedProcessInstruction,
                                         SynExpr.CreateLongIdent (SynLongIdent.CreateString "x")
                                     )
                                 )
@@ -303,14 +304,19 @@ module internal CataGenerator =
     /// Get the fields of this particular union case, and describe their relation to the
     /// recursive knot of user-provided DUs for which we are creating a cata.
     let analyse
+        (availableGenerics : SynTyparDecl list)
         (allRecordTypes : SynTypeDefn list)
         (allUnionTypes : SynTypeDefn list)
         (argIndex : int)
         (fields : AdtNode list)
         : CataUnionBasicField list
         =
+        let availableGenerics =
+            availableGenerics
+            |> List.map (fun (SynTyparDecl.SynTyparDecl (_, SynTypar.SynTypar (ident, _, _))) -> ident)
+
         let rec go (prefix : string) (name : Ident option) (ty : SynType) : CataUnionBasicField =
-            let dealWithPrimitive (typeArgs : SynType list option) (ty : SynType) (typeName : LongIdent) =
+            let dealWithPrimitive (typeArgs : int list option) (ty : SynType) (typeName : LongIdent) =
                 let key = typeName |> List.map _.idText |> String.concat "/"
 
                 let isKnownUnion =
@@ -341,7 +347,7 @@ module internal CataGenerator =
                         RequiredGenerics = typeArgs
                     }
 
-            let rec dealWithType (typeArgs : SynType list option) (stripped : SynType) =
+            let rec dealWithType (typeArgs : int list option) (stripped : SynType) =
                 match stripped with
                 | ListType child ->
                     let gone = go (prefix + "_") None child
@@ -382,7 +388,20 @@ module internal CataGenerator =
                 | SynType.App (ty, _, childTypeArgs, _, _, _, _) ->
                     match typeArgs with
                     | Some _ -> failwithf "Nested applications of types not supported in %+A" ty
-                    | None -> dealWithType (Some childTypeArgs) (SynType.stripOptionalParen ty)
+                    | None ->
+                        let childTypeArgs =
+                            childTypeArgs
+                            |> List.map (fun generic ->
+                                let generic =
+                                    match generic with
+                                    | SynType.Var (SynTypar.SynTypar (name, _, _), _) -> name
+                                    | _ -> failwithf "Unrecognised generic arg: %+A" generic
+
+                                availableGenerics
+                                |> List.findIndex (fun knownGeneric -> knownGeneric.idText = generic.idText)
+                            )
+
+                        dealWithType (Some childTypeArgs) (SynType.stripOptionalParen ty)
                 | SynType.LongIdent (SynLongIdent.SynLongIdent (ty, _, _)) -> dealWithPrimitive typeArgs stripped ty
                 | SynType.Var (typar, _) ->
                     {
@@ -457,6 +476,8 @@ module internal CataGenerator =
                 {
                     Name = name |> Option.map Ident.lowerFirstLetter
                     Type = ty
+                    // TODO this is definitely wrong
+                    GenericsOfParent = []
                 }
             )
 
@@ -499,6 +520,7 @@ module internal CataGenerator =
                                     false,
                                     range0
                                 )
+                        GenericsOfParent = union.Typars
                     }
                     |> List.singleton
             }
@@ -511,12 +533,28 @@ module internal CataGenerator =
 
     /// Build the DU which defines the states our state machine can be in.
     let createInstructionType (analysis : UnionAnalysis list) : SynTypeDefn =
+        let parentGenerics =
+            analysis
+            |> List.collect _.Typars
+            |> List.map (fun (SynTyparDecl.SynTyparDecl (_, SynTypar.SynTypar (ident, _, _))) -> ident.idText)
+            |> List.distinct
+            |> List.map (fun i ->
+                SynTyparDecl.SynTyparDecl ([], SynTypar.SynTypar (Ident.Create i, TyparStaticReq.None, false))
+            )
+
         // One union case for each union type, and then
         // a union case for each union case which contains a recursive reference.
         let casesFromProcess : SynUnionCase list =
             baseCases analysis
             |> List.map (fun unionCase ->
-                SynUnionCase.Create (unionCase.Name, unionCase.Fields |> List.map (fun f -> SynField.Create f.Type))
+                let fields =
+                    unionCase.Fields
+                    |> List.map (fun field ->
+                        // TODO: adjust type parameters
+                        SynField.Create field.Type
+                    )
+
+                SynUnionCase.Create (unionCase.Name, fields)
             )
 
         let casesFromCases =
@@ -528,14 +566,22 @@ module internal CataGenerator =
         let cases = casesFromProcess @ casesFromCases
 
         let typars =
-            // TODO: deduplicate names where we have the same generic across multiple DUs
-            analysis
-            |> List.collect _.Typars
-            |> fun x ->
-                if x.IsEmpty then
-                    None
-                else
-                    Some (SynTyparDecls.PostfixList (x, [], range0))
+            let count = analysis |> List.map (fun x -> List.length x.Typars) |> List.max
+
+            if analysis |> List.forall (fun x -> x.Typars.IsEmpty) then
+                None
+            else
+
+            let typars =
+                analysis
+                |> List.collect _.Typars
+                |> List.map (fun (SynTyparDecl.SynTyparDecl (_, SynTypar.SynTypar (ident, _, _))) -> ident.idText)
+                |> List.distinct
+                |> List.map (fun i ->
+                    SynTyparDecl.SynTyparDecl ([], SynTypar.SynTypar (Ident.Create i, TyparStaticReq.None, false))
+                )
+
+            Some (SynTyparDecls.PostfixList (typars, [], range0))
 
         SynTypeDefn.SynTypeDefn (
             SynComponentInfo.SynComponentInfo (
@@ -633,7 +679,26 @@ module internal CataGenerator =
                                         [ SynType.Var (generics.[getNameKeyUnion ty], range0) ],
                                         true
                                     )
-                                | FieldDescription.NonRecursive ty -> ty
+                                | FieldDescription.NonRecursive ty ->
+                                    match field.RequiredGenerics with
+                                    | None -> ty
+                                    | Some generics ->
+                                        let generics =
+                                            generics
+                                            |> List.map (fun i ->
+                                                let (SynTyparDecl.SynTyparDecl (_, typar)) = analysis.Typars.[i]
+                                                SynType.Var (typar, range0)
+                                            )
+
+                                        SynType.App (
+                                            ty,
+                                            Some range0,
+                                            generics,
+                                            List.replicate (generics.Length - 1) range0,
+                                            Some range0,
+                                            false,
+                                            range0
+                                        )
 
                             SynType.Fun (
                                 SynType.SignatureParameter (
@@ -720,7 +785,11 @@ module internal CataGenerator =
 
                 let userInputGenerics =
                     analysis.Typars
-                    |> List.map (fun (SynTyparDecl.SynTyparDecl (_, typar)) -> SynType.Var (typar, range0))
+                    |> List.map (fun (SynTyparDecl.SynTyparDecl (_, SynTypar.SynTypar (ident, _, _))) -> ident.idText)
+                    |> List.distinct
+                    |> List.map (fun i ->
+                        SynType.Var (SynTypar.SynTypar (Ident.Create i, TyparStaticReq.None, false), range0)
+                    )
 
                 let ty =
                     SynType.App (
@@ -751,9 +820,11 @@ module internal CataGenerator =
         // A "real" generic for each generic in the user-provided type
         let genericsFromUserInput =
             analysis
-            |> List.collect (fun analysis ->
-                // TODO: deduplicate generics with the same name from different cases
-                analysis.Typars
+            |> List.collect _.Typars
+            |> List.map (fun (SynTyparDecl.SynTyparDecl (_, SynTypar.SynTypar (ident, _, _))) -> ident.idText)
+            |> List.distinct
+            |> List.map (fun i ->
+                SynTyparDecl.SynTyparDecl ([], SynTypar.SynTypar (Ident.Create i, TyparStaticReq.None, false))
             )
 
         let genericsFromCata =
@@ -806,21 +877,18 @@ module internal CataGenerator =
                         prod.Fields
                         |> List.indexed
                         |> List.collect (fun (i, node) ->
-                            let availableGenerics =
-                                match node.Type with
-                                | SynType.App (_, _, vars, _, _, _, _) -> vars
-                                | _ -> []
-
                             match getNameUnion node.Type with
                             | None ->
-                                analyse allRecordTypes allUnionTypes i [ node ] |> List.map CataUnionField.Basic
+                                analyse typars allRecordTypes allUnionTypes i [ node ]
+                                |> List.map CataUnionField.Basic
                             | Some name ->
 
                             match Map.tryFind (List.last(name).idText) recordTypes with
                             | None ->
-                                analyse allRecordTypes allUnionTypes i [ node ] |> List.map CataUnionField.Basic
+                                analyse typars allRecordTypes allUnionTypes i [ node ]
+                                |> List.map CataUnionField.Basic
                             | Some fields ->
-                                List.zip fields (analyse allRecordTypes allUnionTypes i fields)
+                                List.zip fields (analyse typars allRecordTypes allUnionTypes i fields)
                                 |> List.map (fun (field, analysis) -> Option.get field.Name, analysis)
                                 |> CataUnionField.Record
                                 |> List.singleton
@@ -1310,16 +1378,20 @@ module internal CataGenerator =
                 None
             )
 
-        // A generic for each DU case, and a generic for each generic in the DU
-        let genericCount = analysis.Length + (analysis |> List.sumBy _.Typars.Length)
+        let userSuppliedGenerics =
+            analysis
+            |> List.collect _.Typars
+            |> List.map (fun (SynTyparDecl.SynTyparDecl (_, SynTypar.SynTypar (ident, _, _))) -> ident.idText)
+            |> List.distinct
+            |> List.map (fun i -> SynTypar.SynTypar (Ident.Create i, TyparStaticReq.None, false))
 
         let instructionsArrType =
-            if genericCount > analysis.Length then
+            if not userSuppliedGenerics.IsEmpty then
                 SynType.App (
                     SynType.CreateLongIdent "Instruction",
                     Some range0,
-                    List.replicate (genericCount - analysis.Length) (SynType.Anon range0),
-                    List.replicate (genericCount - analysis.Length - 1) range0,
+                    userSuppliedGenerics |> List.map (fun x -> SynType.Var (x, range0)),
+                    List.replicate (userSuppliedGenerics.Length - 1) range0,
                     Some range0,
                     false,
                     range0
@@ -1327,6 +1399,14 @@ module internal CataGenerator =
             else
                 SynType.CreateLongIdent "Instruction"
 
+        let cataGenerics =
+            [
+                for generic in userSuppliedGenerics do
+                    yield SynType.Var (generic, range0)
+                for case in analysis do
+                    yield SynType.Var (SynTypar.SynTypar (case.GenericName, TyparStaticReq.None, false), range0)
+            ]
+
         let headPat =
             SynPat.LongIdent (
                 SynLongIdent.CreateString "loop",
@@ -1340,8 +1420,8 @@ module internal CataGenerator =
                                 SynType.App (
                                     SynType.CreateLongIdent (SynLongIdent.CreateFromLongIdent [ cataTypeName ]),
                                     Some range0,
-                                    List.replicate genericCount (SynType.Anon range0),
-                                    List.replicate (genericCount - 1) range0,
+                                    cataGenerics,
+                                    List.replicate (cataGenerics.Length - 1) range0,
                                     Some range0,
                                     false,
                                     range0
@@ -1456,7 +1536,20 @@ module internal CataGenerator =
                             SynPat.Named (SynIdent.SynIdent (unionCase.StackName, None), false, None, range0),
                             None,
                             SynExpr.CreateApp (
-                                SynExpr.CreateLongIdent (SynLongIdent.CreateString "ResizeArray"),
+                                SynExpr.TypeApp (
+                                    SynExpr.CreateIdent (Ident.Create "ResizeArray"),
+                                    range0,
+                                    [
+                                        SynType.Var (
+                                            SynTypar.SynTypar (unionCase.GenericName, TyparStaticReq.None, false),
+                                            range0
+                                        )
+                                    ],
+                                    [],
+                                    Some range0,
+                                    range0,
+                                    range0
+                                ),
                                 SynExpr.CreateConst SynConst.Unit
                             ),
                             range0,
@@ -1526,14 +1619,20 @@ module internal CataGenerator =
                 |> fun x -> SynType.Var (x, range0)
             )
 
-        let userProvidedGenerics = analysis |> List.collect (fun x -> x.Typars)
-
-        let runFunctions =
-            List.zip allUnionTypes allTypars
-            |> List.map (fun (unionType, relevantTypar) ->
-                createRunFunction cataName userProvidedGenerics allTypars relevantTypar unionType
+        let userProvidedGenerics =
+            analysis
+            |> List.collect _.Typars
+            |> List.map (fun (SynTyparDecl (_, SynTypar.SynTypar (ident, _, _))) -> ident.idText)
+            |> List.distinct
+            |> List.map (fun x ->
+                SynTyparDecl.SynTyparDecl ([], SynTypar.SynTypar (Ident.Create x, TyparStaticReq.None, false))
             )
 
+        let runFunctions =
+            List.zip analysis allTypars
+            |> List.map (fun (analysis, relevantTypar) ->
+                createRunFunction cataName userProvidedGenerics allTypars relevantTypar analysis
+            )
 
         let cataStructures =
             createCataStructure analysis