Compose records in arg parser (#234)

WoofWare.Myriad.Plugins/Teq.fs

@@ -0,0 +1,18 @@
+namespace WoofWare.Myriad.Plugins
+
+// Extracted from https://github.com/G-Research/TypeEquality
+// which is Apache-2.0 licenced. See `TeqLicence.txt`.
+// We inline this code because Myriad doesn't seem to reliably load package references in the generator.
+// I have reformatted a little, and stripped out all the code I don't use.
+
+type internal Teq<'a, 'b> = private | Teq of ('a -> 'b) * ('b -> 'a)
+
+[<RequireQualifiedAccess>]
+module internal Teq =
+
+    let refl<'a> : Teq<'a, 'a> = Teq (id, id)
+    let cast (Teq (f, _)) a = f a
+
+    [<RequireQualifiedAccess>]
+    module Cong =
+        let believeMe<'a, 'b, 'a2, 'b2> (_ : Teq<'a, 'b>) : Teq<'a2, 'b2> = unbox <| (refl : Teq<'a2, 'a2>)