[mercury-users] Proposed change to char literal syntax

[Ian MacLarty]

On Mon, Oct 02, 2006 at 01:36:40PM +1000, Ralph Becket wrote:
> The current syntax for char literals has a number of problems and we
> would like to gauge user opinion on making a change.
> 
> Currently, the syntax for a character literal is to just type the
> character as is (e.g., a, b, c), except
> - if it's also an operator name (e.g., +, *, /) in which case
>   you need to place it in parentheses (e.g., (+), (*), (/))
> - or if it's otherwise used in Merury programs (e.g., ', ", space)
>   in which case you need to place it in single quotes and possibly
>   escape it (e.g., '\'', '"', ' ')
> - or if it's a non-printable character, in which case you need to
>   quote and use a character escape sequence (e.g., '\n', '\t', '\0234').
> 
> We think you'll agree it's something of a mess.  Worse, the type checker
> can run out of stack processing erroneous Mercury code containing single
> character function symbols (each such symbol doubles the space of
> potential type assignments, one being a character, the other being the
> function symbol).  This leads to an exponential amount of work which can
> cause the compiler to run out of stack space in some cases.
> 
> Before we try to fix the situation, we'd like to find out how badly such
> a change would affect users.  If we see wailing and gnashing of teeth on
> this list from enough users then we will probably abandon the plan...
> otherwise it would be good to fix up this syntactic wart.
> 

You haven't said what the proposed change is.

Ian.
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