ISSUE: Keyword/Expression Simplification

REVISION HISTORY: 17 Feb 1994, William Lott (Gwydion)

RELATED ISSUES:
Symbol Literal Cleanups
    This proposal assumes Symbol Literal Cleanups passes.  If Symbol
    Literal Cleanups is not accepted, this proposal will have to be
    adjusted to correspond to whatever takes the place of Symbol Literal
    Cleanups.


CATEGORY: Change

PROBLEM DESCRIPTION:

The rules for where keywords can appear as literals in expressions are
unnecessarily complex, for little gain in utility.  Having to explain that:

	foo(keyword:)

is syntactically valid while:

	if (var = keyword:)
	  ...
	end

is not is going to make the language just that much more complex to and
difficult to learn by potential users.


PROPOSAL:

Remove the grammar statement that allows keywords to be used as
expressions, reducing the expression grammar non-terminal to:

    expression:
	operand
	operand binop-series

RATIONALE:

Removing the special case for keywords as expressions will simplify the
language without sacrificing any functionality.  Any place a symbolic
literal is needed, the #"..." syntax can be used instead.

EXAMPLES:

    var = foo:;
    => syntax error, as always

    var = #"foo";
    => #t or #f, depending on var.

    (foo:) = 10;
    => now a syntax error, was okay before.

COST TO IMPLEMENTORS:

Minor.  Requires a few simple changes to the grammar.

COST TO USERS:

Requires that symbolic constants be #"foo" a few places where foo: would
have otherwise worked.

PERFORMANCE IMPACT:

BENEFITS:

Makes the language slightly easier to understand.

AESTHETICS:

Positive.

IMPLEMENTATION NOTES:

FUTURE FEATURES:

DISCUSSION:

VOTES:


OPTIONAL AMENDMENT:

Extend the property-list grammar non-terminal to:

    property-list:
	property
	property-list , property

    property:
	keyword expression
	keyword keyword

RATIONALE:

Some people have complained that for init-keywords, having the syntax of
the keyword specification be identical to uses of the keyword in the
argument list to make is good.  Specifically, they prefer:

    define class <foo> (<object>)
      slot bar, init-keyword: bar:;
    end;

to:

    define class <foo> (<object>)
      slot bar, init-keyword: #"bar";
    end;

This amendment allows for this by special casing property lists, as opposed
to expressions.  The foot-print of this special case is much smaller, and
hence impacts less of the overall language.

EXAMPLES:

No net change to define class.

COST TO IMPLEMENTORS:

Minor.  Requires a few simple changes to the grammar.

COST TO USERS:

Requires that they understand that the things in property lists can be
keywords in addition to expressions.

PERFORMANCE IMPACT:

BENEFITS:

Makes init-keyword: properties in class slots easier to read.

AESTHETICS:

Depends on opinion.

IMPLEMENTATION NOTES:

FUTURE FEATURES:

DISCUSSION:

VOTES: