0004838: Treat let-module expressions as non-expansive where possible

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Date Submitted

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0004838

OCaml

OCaml general

public

2009-07-20 12:58

2012-06-01 10:10

Reporter

yallop

Assigned To

garrigue

Priority

normal

Severity

feature

Reproducibility

always

Status

closed

Resolution

fixed

Platform

OS Version

Product Version

3.11.1

Target Version

Fixed in Version

4.00.0+dev

Summary

0004838: Treat let-module expressions as non-expansive where possible

Description

Expressions of the form

let module M = <module-expr> in e

are currently always treated as expansive by the type checker. As a result, in the following declaration "id" is given a non-polymorphic type:

let id = let module M = struct end in fun x -> x

(There are, of course, useful examples as well, particularly where the module expression declares types.)

It seems that many such expressions (including all those where the module-expr is built from non-expansive terms) could be safely treated as non-expansive, increasing the number of typeable programs.

Additional Information

Patch against 3.11.1 attached.

Tags

No tags attached.

Attached Files

let_module_expansivity.patch [^] (1,432 bytes) 2009-07-20 12:58 [Show Content] [Hide Content]

--- typing/typecore.ml.orig	2009-07-20 11:54:57.000000000 +0100
+++ typing/typecore.ml	2009-07-20 11:54:57.000000000 +0100
@@ -652,8 +652,36 @@
       Vars.fold (fun _ (mut,_,_) b -> decr count; b && mut = Immutable)
         vars true &&
       !count = 0
+  | Texp_letmodule (id, modl, body) ->
+      is_nonexpansive_module modl && 
+        is_nonexpansive body
   | _ -> false
 
+and is_nonexpansive_module mexp = 
+  match mexp.mod_desc with
+    Tmod_ident _ -> true
+  | Tmod_structure s -> List.for_all is_nonexpansive_structure_item s
+  | Tmod_functor (_, _, _) -> true
+  | Tmod_apply (_, _, _) -> false
+  | Tmod_constraint (modexp, _, _) -> is_nonexpansive_module mexp
+
+and is_nonexpansive_structure_item = function
+    Tstr_eval e -> is_nonexpansive e
+  | Tstr_value (rec_flag, pat_exp_list) -> 
+      List.for_all (fun (pat, exp) -> is_nonexpansive exp) pat_exp_list
+  | Tstr_primitive _ -> true
+  | Tstr_type _ -> true
+  | Tstr_exception _ -> true
+  | Tstr_exn_rebind _ -> true
+  | Tstr_module (_, modexp) -> is_nonexpansive_module modexp
+  | Tstr_recmodule mods ->
+      List.for_all (fun (id, modexp) -> is_nonexpansive_module modexp) mods
+  | Tstr_modtype _ -> true
+  | Tstr_open _ -> true
+  | Tstr_class _ -> false
+  | Tstr_cltype _ -> true
+  | Tstr_include (modexp, ids) -> is_nonexpansive_module modexp
+
 and is_nonexpansive_opt = function
     None -> true
   | Some e -> is_nonexpansive e

Relationships

related to

0004511

closed

garrigue

Local modules remove polymorphism.

Notes
(0007494) garrigue (manager) 2012-06-01 09:24 edited on: 2012-06-01 10:10	Fixed in trunk and 4.00, revisions 12535, 12536. The code was already there for first-class modules.

Issue History
Date Modified	Username	Field	Change
2009-07-20 12:58	yallop	New Issue
2009-07-20 12:58	yallop	File Added: let_module_expansivity.patch
2009-08-25 15:23	xclerc	Relationship added	related to 0004511
2011-05-31 16:22	doligez	Status	new => acknowledged
2012-06-01 09:24	garrigue	Note Added: 0007494
2012-06-01 09:24	garrigue	Status	acknowledged => closed
2012-06-01 09:24	garrigue	Assigned To	=> garrigue
2012-06-01 09:24	garrigue	Resolution	open => fixed
2012-06-01 09:24	garrigue	Fixed in Version	=> 3.12.0
2012-06-01 10:10	garrigue	Fixed in Version	3.12.0 => 4.00.0+dev
2012-06-01 10:10	garrigue	Note Edited: 0007494	View Revisions