Issue FORMAT-ATSIGN-COLON Writeup

Issue:        FORMAT-ATSIGN-COLON

References:   FORMAT description (p386)

Category:     CLARIFICATION

Edit history: Version 1 by Pitman 02/27/87

              Version 2 by cleanup committee 15-Mar-87

              Version 3 by Masinter 15-Mar-87

	      Version 4 by Masinter  5-Jun-87


Problem Description:


CLtL describes the format op syntax as:


"a format directive consists of a tilde (~), optional prefix parameters

separated by commas, optional colon (:) and atsign (@) modifiers, and a

single character indicating what kind of directive this is."


CLtL uses :@ fairly consistently throughout without saying whether @: is

legal. Is @: allowed?


Proposal (FORMAT-ATSIGN-COLON:OK):


There is no required ordering between the @ and : modifier.


Rationale:


This is currently underspecified, and this way of specifying it will

cause the least disruption to user code.


Current practice:


Most implementations accept these in either order. Some implementations

have been known to expect only :@.


Adoption Cost:


The change to accept either syntax is probably quite trivial.


Benefits:


Having @: and :@ mean different things would be awkward. 


Conversion Cost:


Existing user code would be unaffected.


Aesthetics:


Leaving these unordered is slightly simpler conceptually.


Discussion:


The cleanup committee supports this clarification.