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Feature Request: Error message for 'Illegal permutation of structure fields' #3819

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vicuna opened this issue Oct 24, 2005 · 4 comments · Fixed by #8546

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@vicuna
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commented Oct 24, 2005

Original bug ID: 3819
Reporter: administrator
Status: acknowledged
Resolution: open
Priority: normal
Severity: feature
Category: typing
Monitored by: @gasche

Bug description

Full_Name: Ethan Aubin
Version: 3.08.4
OS: linux
Submission from: c-24-60-21-144.hsd1.ma.comcast.net (24.60.21.144)

I came across an error saying 'Illegal permutation of structure fields'. The
modules I'm working with are have interfaces ~ 150 lines and its hard to figure
out whats in the wrong spot. Could the message print an which fields are
conflicting (omitting the rest)? Thanks -EA

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@vicuna

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commented Feb 18, 2015

Comment author: @zoggy

Ping.

@vicuna

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commented Feb 18, 2015

Comment author: @gasche

Would someone feel motivated to provide a small representative program that displays this warning?

@vicuna

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commented Feb 18, 2015

Comment author: @yallop

Here's an example. The problem boils down to incompatibility between module type members when checking signature inclusion compatibility:

   # module F (X : sig module type T = sig val x : int val y : int end end) =
              (X : sig module type T = sig val y : int val x : int end end);;
     Characters 85-86:
                (X : sig module type T = sig val y : int val x : int end end);;
                 ^
   Error: Signature mismatch:
          Modules do not match:
            sig module type T = sig val x : int val y : int end end
          is not included in
            sig module type T = sig val y : int val x : int end end
          Module type declarations do not match:
            module type T = sig val x : int val y : int end
          does not match
            module type T = sig val y : int val x : int end
          At position module type T = <here>
          Illegal permutation of structure fields
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commented Feb 18, 2015

Comment author: @zoggy

Here are four files.
When compiling order.mli and order.ml, the error message:

File "order.ml", line 1:
Error: The implementation order.ml does not match the interface order.cmi:
       ...
       At position module type M = <here>
       Illegal permutation of structure fields

When compiling order_m.mli and order_m.ml:

File "order_m.ml", line 1:
Error: The implementation order_m.ml
       does not match the interface order_m.cmi:
       Module type declarations do not match:
         module type M =
           sig
             module T : sig type t = string end
             module T2 : sig val foo : int -> string end
           end
       does not match
         module type M =
           sig
             module T2 : sig val foo : int -> string end
             module T : sig type t = string end
           end
       At position module type M = <here>
       Illegal permutation of structure fields
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