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."