0000055: typeclass instances for e.g. bag(T) no longer work

View Issue Details [ Jump to Notes ]

[ Issue History ] [ Print ]

Project

Category

View Status

Date Submitted

Last Update

0000055

mercury

Bug

public

2008-03-29 02:38

2008-06-02 15:06

Reporter

obo

Assigned To

Priority

normal

Severity

major

Reproducibility

always

Status

confirmed

Resolution

open

Product Version

Target Version

Fixed in Version

Summary

0000055: typeclass instances for e.g. bag(T) no longer work

Description

with rotd-2008-03-27, the attached file bug.m gives the following error:

bug.m:001: Warning: interface for module `bug' does not export anything.
bug.m:011: In instance declaration for `bug.fooable((bag.bag(V)))':
bug.m:011: the first arg contains a type variable which is used in another
bug.m:011: arg

with rotd-2007-08-13, the same code was compilable and worked as expected.

When I tried to avoid the type variable by instantiating the typeclass for eg. bag(string) specifically, the recent ROTD gives me this error:

testhugemap.m:047: In instance declaration for
testhugemap.m:047: `pickle.tc_picklable((bag.bag(string)))':
testhugemap.m:047: the first arg is a type whose first arg is not a variable

What is the correct way of instantiating such typeclasses?

Thanks, Ondrej.

Tags

No tags attached.

Attached Files

bug.m (206 bytes) 2008-03-29 02:38

Relationships

Relationships

Notes
~0000096 mark (administrator) 2008-03-29 12:00	The basic problem is the following restriction from the reference manual: "The types in an instance declaration must not be abstract types which are elsewhere defined as equivalence types." bag/1 is an abstract type that happens to be defined as an equivalence type. The error message is just plain wrong, however.

~0000103 juliensf (administrator) 2008-06-02 15:06	I have changed the definition of bag/1 so that it can be used in type class instances -- the issue with the error message is still a bug though.

Notes

Date Modified	Username	Field	Change
Issue History
2008-03-29 02:38	obo	New Issue
2008-03-29 02:38	obo	File Added: bug.m
2008-03-29 12:00	mark	Note Added: 0000096
2008-03-29 12:02	mark	Status	new => confirmed
2008-06-02 15:06	juliensf	Note Added: 0000103

Issue History