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GADT with polymorphic variants bug #5948

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vicuna opened this Issue Mar 12, 2013 · 1 comment

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commented Mar 12, 2013

Original bug ID: 5948
Reporter: @lpw25
Assigned to: @garrigue
Status: closed (set by @xavierleroy on 2015-12-11T18:18:41Z)
Resolution: fixed
Priority: normal
Severity: minor
Version: 4.00.1
Fixed in version: 4.00.2+dev
Category: typing
Child of: #5998
Monitored by: @gasche

Bug description

I came across a typing bug while playing around with GADTs and polymorphic variants. The following code produces a segmentation fault:

type tag = [TagA | TagB | `TagC]

type 'a poly =
AandBTags : [< TagA of int | TagB ] poly
| ATag : [< TagA of int] poly constraint 'a = [< TagA of int | `TagB]

let intA = function TagA i -> i let intB = function TagB -> 4

let intAorB = function
TagA i -> i | TagB -> 4

type _ wrapPoly =
WrapPoly : 'a poly -> ([< TagA of int | TagB] as 'a) wrapPoly

let example6 : type a. a wrapPoly -> (a -> int) =
fun w ->
match w with
| WrapPoly ATag -> intA
| WrapPoly _ -> intA (* This should not be allowed *)

let _ = example6 (WrapPoly AandBTags) `TagB (* This causes a seg fault *)

@vicuna

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commented Mar 13, 2013

Comment author: @garrigue

Fixed in trunk and 4.00, revisions 13396 and 13397.

Note: you cannot refine variant types whose row variable is rigid.

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