JJ: Description from the destination commit:

wip polymorphic error

JJ: Description from source commit:
.

src/crypto.ml

@@ -10,15 +10,23 @@ module EddsaPublicKey = struct
   type t = pub
 
   let to_octets t = pub_to_octets t
-  let of_octets t = pub_of_octets t |> Result.get_ok
-  let bin = Bin.map (Bin.bytes 32) of_octets to_octets
+
+  let of_octets t =
+    pub_of_octets t |> function
+    | Error e -> Fmt.error "%a" Mirage_crypto_ec.pp_error e
+    | Ok v -> Ok v
+
+  let bin =
+    let of_octets o =
+      match of_octets o with Error e -> raise (Util.Bin_error e) | Ok v -> v
+    in
+    Bin.map (Bin.bytes 32) of_octets to_octets
 
   let of_b32 s =
     let open Syntax in
     let* octets = B32.decode s in
-    match pub_of_octets octets with
-    | Error e -> Fmt.error "%a" Mirage_crypto_ec.pp_error e
-    | Ok pub -> Ok pub
+    let* pub = of_octets octets in
+    Ok pub
 
   let to_b32 t = B32.encode (to_octets t)
   let jsont = Jsont.of_of_string ~kind:"EddsaPublicKey" of_b32 ~enc:to_b32

src/pg.ml

@@ -38,7 +38,7 @@ module Caqti_type = struct
     let open EddsaPublicKey in
     custom
       ~encode:(fun v -> Ok (to_octets v))
-      ~decode:(fun v -> Ok (of_octets v))
+      ~decode:(fun v -> of_octets v)
       octets
 
   let eddsa_signature : EddsaSignature.t t =

src/util.ml

@@ -1,3 +1,5 @@
+exception Bin_error of string
+
 (* TODO bin
    - no [Bin.of_string] ? *)
 let bin_of_string bin s =