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(*
Copyright © 2012 MLstate
This file is part of Opa.
Opa is free software: you can redistribute it and/or modify it under the
terms of the GNU Affero General Public License, version 3, as published by
the Free Software Foundation.
Opa is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for
more details.
You should have received a copy of the GNU Affero General Public License
along with Opa. If not, see <http://www.gnu.org/licenses/>.
*)
(*
@author Niki Vazou
*)
(* ************************************************************************** *)
(** {b Descr}: This module implements the @extendwith directive stuff. *)
(* ************************************************************************** *)
exception Extend_with_failure of bool
(* ************************************************************************** *)
(** {b Descr} : This function adds a field to a record or a sum containing
only one case. If the type is a typename, it unfolds it to apply
this process.
This function process the type in surface, i.e. it does not open the
records nested in the type sub-terms. This means that if the type is not
a record of a sum with only one case, this function generates an error.
This function is used to implements typechecking of the @extendwith
directive.
@raise Extend_with_failure
{b Visibility} : Not exported outside this module. *)
(* ************************************************************************** *)
let extend_record_simple_type env initial_ty field_name field_type =
let rec rec_extend seen_expansions ~dont_expand ty =
(* First, get the canonical representation of the type. *)
let ty = W_CoreTypes.simple_type_repr ty in
match ty.W_Algebra.sty_mark with
| W_Algebra.TM_row_open_seen -> ty
| W_Algebra.TM_not_seen -> (
(* Mark the type as already seen before going on to prevent looping. *)
ty.W_Algebra.sty_mark <- W_Algebra.TM_row_open_seen ;
match ty.W_Algebra.sty_desc with
| W_Algebra.SType_var _ ->
(* Trying to open something not being a record type. This
should not happen except on type variables not yet instantiated.
If it is a type variable not yet instantiated, then may be if the
user add the right type constraint this variable will get
instantiated and the opening will succeed. So, emit an error
message suggesting to explicitly coerce the typed expression. *)
raise (Extend_with_failure true)
| W_Algebra.SType_named named -> (
(* Since a name is not a structure, we must directly open the
manifest representation of this named type. *)
match named.W_Algebra.nst_unwinded with
| Some manifest ->
let opened_manifest =
rec_extend seen_expansions ~dont_expand: false manifest in
(* Attention, by opening a named type, we must forget this
name because this name represents a type **non** opened. So
we return a new type that is directly the opened manifest
representation of the initial type. *)
opened_manifest
| None ->
if dont_expand then (
(* The named type has no manifest representation. Hence it is
purely abstract and has no structure. Extending "fails". *)
raise (Extend_with_failure false)
)
else (
let (_, seen_expansions') = (* TODO: May be dont_expand no more useful if this function is refactored according to new unification with heights. *)
W_TypeAbbrevs.incrementally_expand_abbrev
env seen_expansions ty in
ty.W_Algebra.sty_mark <- W_Algebra.TM_not_seen ;
rec_extend seen_expansions' ~dont_expand: true ty
)
)
| W_Algebra.SType_sum_of_records sumcases_column -> (
let sumcases_column =
W_CoreTypes.column_type_repr sumcases_column in
let (col_rows, _) = sumcases_column.W_Algebra.ct_value in
(* Not that we do not take into account the ending of the column.
This means that it is possible that it is a column variable that
will be later instantiated by some other rows. If at the present
moment we really have one unique row, then opening will work,
other rows will be added afterwards although if they were added
before (before the unification constraint arrived sooner) the
opening would have failed.
This is another case where this construct doesn't commute ! *)
match col_rows with
| [unique_row] -> (
let unique_row = W_CoreTypes.row_type_repr unique_row in
let (row_fields, row_ending) = unique_row.W_Algebra.rt_value in
(* Rebuild a row type, adding the new field and if applied
deleting a previous with the same name. *)
let new_fields = (field_name, field_type)::
(List.filter (fun (x, _) -> not(x=field_name)) row_fields) in
let extended_row = {
W_Algebra.rt_value = (new_fields, row_ending)
} in
(* Finally, rebuild a column replacing its row and forcing
it ending to be closed. *)
let final_ty =
{ W_Algebra.sty_desc =
W_Algebra.SType_sum_of_records
{ W_Algebra. ct_value =
([extended_row], W_Algebra.Closed_column) };
W_Algebra.sty_link = None ;
W_Algebra.sty_mark = W_Algebra.TM_not_seen }
in
W_TypeInfo.add_linked_object
final_ty.W_Algebra.sty_desc
ty.W_Algebra.sty_desc ;
final_ty
)
| _ ->
(* If the column has several cases, then it is not a record,
it is rather a sum. Hence, in this case we emit an error. *)
raise (Extend_with_failure false)
)
| W_Algebra.SType_forall _
| W_Algebra.SType_arrow (_, _) ->
raise (Extend_with_failure false)
)
| _ (* Other markers. *) -> assert false in
(* Effective body of the function [extend_record_simple_type]. *)
let extended_ty =
rec_extend W_TypeAbbrevs.empty_memory ~dont_expand: false initial_ty in
W_CoreTypes.cleanup_simple_type initial_ty ;
extended_ty
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