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Issue SYMBOL-MACROLET-DECLARE Writeup

Issue:         SYMBOL-MACROLET-DECLARE

References: SYMBOL-MACROLET (88-002R page 2-81)

WITH-ACCESSORS (88-002R page 2-88)

WITH-SLOTS (88-002R page 2-92)

Related Issues: SYMBOL-MACROLET-SEMANTICS

FLET-DECLARATIONS (passed)

Category: ADDITION

Edit history: Version 1, 12-Sep-88, Moon

Version 2, 9-Dec-88, Masinter

(add cross reference, discussion)

Problem description:

It would be both natural and nice to be able to write

(with-slots (rho theta) point

(declare (single-float rho theta))

...computation...)

Proposal (SYMBOL-MACROLET-DECLARE:ALLOW):

Allow declarations at the head of the body of SYMBOL-MACROLET, and hence

in WITH-ACCESSORS and WITH-SLOTS. Exactly the same declarations are

allowed as for LET, with one exception: SYMBOL-MACROLET signals an error

if a SPECIAL declaration names one of the symbols being defined as a

symbol-macrolet. A type declaration of one of these symbols is equivalent

to wrapping a THE expression around the expansion of that symbol.

Example:

See problem description.

Rationale:

If SYMBOL-MACROLET is intended to resemble LET in syntax, it ought to

allow declarations. When writing a SYMBOL-MACROLET directly, the user

could just as easily write a THE expression instead of a type

declaration. However, when invoking a macro such as WITH-SLOTS that

expands into SYMBOL-MACROLET, the user does not have this option since

the expansion is not supplied explicitly by the user.

Current practice:

SYMBOL-MACROLET was only tentatively added to Common Lisp 3 months ago.

Cost to Implementors:

Less than one man-hour.

Cost to Users:

None.

Cost of non-adoption:

Minor wart in the language.

Benefits:

More consistent language definition.

Esthetics:

More consistent language definition.

Discussion:

This issue is related to SYMBOL-MACROLET-SEMANTICS.

"A macro-definition for SYMBOL-MACROLET would leave the issue of

DECLARE open. But the special-form version of SYMBOL-MACROLET

really should address it."


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