0000296: ui mode and multiple clauses

View Issue Details [ Jump to Notes ]

[ Issue History ] [ Print ]

Project

Category

View Status

Date Submitted

Last Update

0000296

mercury

Bug

public

2013-07-31 12:58

2014-10-05 17:33

Reporter

wangp

Assigned To

Priority

normal

Severity

minor

Reproducibility

always

Status

new

Resolution

open

Product Version

Target Version

Fixed in Version

Summary

0000296: ui mode and multiple clauses

Description

from Michael:

This code triggers a mode error:

:- mode get_text_content0(in, out, ui) is det.

get_text_content0([], [], _IO).
get_text_content0([Node|Nodes], [Text|Texts], IO) :-
     get_text_content_from_node(Node, Text, IO), % <-- error here for IO
     get_text_content0(Nodes, Texts, IO).

However if I write the switch explicitly, it's fine:

get_text_content0(Nodes, Texts, IO) :-
     (
         Nodes = [],
         Texts = []
     ;
         Nodes = [Node|Nodes0],
         get_text_content_from_node(Node, Text, IO),
         get_text_content0(Nodes0, Texts0, IO),
         Texts = [Text|Texts0]
     ).

Tags

No tags attached.

Attached Files

Relationships

Relationships

Notes

~0000791

mark (administrator)

2014-10-05 17:33

The explanation for this is that the introduction of HeadVars introduces extra unifications, and these cause the ui term to lose its uniqueness according to the mode analyser.

HeadVars are always introduced, but in some cases (such as when a predicate is defined in a single clause) this introduction is reversed in order to retain meaningful variables names in the debugger. A side effect of this reversal is that the mode analyser no longer always chokes.

Using a single clause seems to be an effective workaround for the real bug, which is that the mode analyser doesn't properly keep track of uniqueness.

Notes

Date Modified	Username	Field
Issue History
2013-07-31 12:58	wangp	New Issue
2014-10-05 17:33	mark	Note Added: 0000791

Issue History