# Odd behaviour with ?- expects\_dialect(sicstus)

**URL:** <https://swi-prolog.discourse.group/t/odd-behaviour-with-expects-dialect-sicstus/4217>\
**Category:** Tools\
**Tags:** bug\
**Created:** [July 30, 2021, 2:49pm UTC](https://swi-prolog.discourse.group/t/odd-behaviour-with-expects-dialect-sicstus/4217 "2021-07-30T14:49:36Z")\
**Posts on this page:** 1\
**Showing post:** 10

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**Author:** ![jan](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/jan/32/4_2.png) [@jan](https://swi-prolog.discourse.group/u/jan)\
**Post date:** [August 1, 2021, 7:23am UTC](https://swi-prolog.discourse.group/t/odd-behaviour-with-expects-dialect-sicstus/4217/10 "2021-08-01T07:23:19Z")

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I doubt there is a good solution to this. Indeed, traditionally print/1 does not emit quotes. I think this is wrong. Print/1, using portray/1 is first of all meant for user interaction and notably debugging. All the user-facing tooling (toplevel, debugger, etc.) uses print/1 to print terms. There a were just too many people confused about the exact type of an object that is explicit when quotes are used. Strings make this even worse as it makes `"World"` and `'World'` print the same way.

The main problem with print/portray is that the mechanism is inherently non-modular: any module you may load that adds portray rules may upset the desired way terms are printed.

The normal way to resolve this for a dialect emulation would be to goal expand print/1 to sicstus\_print/1 and then hack a little to temporarily redefine it. In most cases though, print/1 is called through format/3, debug/3 or the toplevel and these are unaware that the desired action originates from SICStus code.

Bottom line is that code should not use print/1 if it wants precise control on how the term is emitted unless we are talking about a stand-alone application where we know the code is never to be combined with any other code.

Prolog output is a mess ☹ Best practice seems to be

- Use format/3 to emit non-term output
- When writing a library, use the print\_message/2 indirection for talking to the user
- Use writeq/1 or write\_canonical/1 to write terms that need to be read by Prolog.
- Use portray\_clause/1 for listing clauses. This predicate must ensure that reading returns the same clause given the same operator declarations).
- Use print/1 only for debug/3 and other interactive use of your program.
- Be careful with portray/1. Only use it for very specific terms for libraries or better, include a dedicated portray library for a specific library. rdf\_portray.pl is such as beast for dealing with RDF.
- write/1 should never have been added to Prolog.

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