Improve the error handling situation (#71)

* Sketches of a condition system

* `Condition.condition` -> `Condition.t`

* Migrate `NT` over

* Migrate `Branch` over

* Migrate `Sublanguage` et al. over

* Migrate the PRL over

* Migrate the DRL over

* Migrate the DML over

* Have `Qualified_name.try_parse` return a `Condition.t`

* Migrate the DDL over

* Migrate the VCL over

* Migrate the SCL over

* Migrate the ICL over

* Migrate the parsers over

* Just inherit the errors from NT and the sublanguages

* Migrate `Management.Physical` over

* Migrate `Configuration` over

* Migrate `Management.Branch` over

* Migrate `Transport` over

* Migrate `System` over

* Migrate `Server` over

* Include messages on on all conditions

* A prettier stringifier

1 files changed, 7 insertions, 4 deletions

diff --git a/lib/scl/parser.ml b/lib/scl/parser.ml
index 3e9c4ed..53719ee 100644
--- a/lib/scl/parser.ml
+++ b/lib/scl/parser.ml
@@ -1,19 +1,22 @@
-type error = ParseError of string
+module Error = struct
+  open Condition
+  let parse_error msg = condition "parse-error" msg empty
+end
 
 let validate = function
   | (Ast.Begin { limit = Some limit; _ } | Ast.Fetch { limit = Some limit; _ })
     when limit <= 0 ->
-      Error (ParseError "The provision of `limit` is expected to be positive.")
+      Error (Error.parse_error "The provision of `limit` is expected to be positive.")
   | stmt -> Ok stmt
 
 let of_sexp sexp =
   match Ast.statement_of_sexp sexp with
-  | exception exn -> Error (ParseError (Printexc.to_string exn))
+  | exception exn -> Error (Error.parse_error (Printexc.to_string exn))
   | stmt -> validate stmt
 
 let of_string s =
   match Sexplib.Sexp.of_string s |> Ast.statement_of_sexp with
-  | exception exn -> Error (ParseError (Printexc.to_string exn))
+  | exception exn -> Error (Error.parse_error (Printexc.to_string exn))
   | stmt -> validate stmt
 
 let to_string stmt = Ast.sexp_of_statement stmt |> Sexplib.Sexp.to_string_hum