Forum: Editorial

References: character printing

Category: CLARIFICATION/CHANGE

Edit history: 2004-07-20, Version 1 by Bruno Haible

Status: For CLiki consideration

Problem Description:

CLHS specifies that when the space character is printed, it prints as "#\ ". This is not what most CL implementations have traditionally done, and brings problems because spaces at the end of line are considered redundant and removed by some text editors.

Proposal (PRINTING-SPACE:TRADITIONAL):

Change the behavior of character printing such that invisible graphic characters such as space can be printed by name.

Test case:

(prin1-to-string #\space) => "#\\Space"

Rationale:

Traditional CL behaviour.

Current practice:

(write #\Space :escape t :pretty nil) writes "#\Space" in CLISP 2.32 and CMUCL release-18e-branch. SBCL 0.8.8.20 and CLISP CVS were changed to write "#\ " instead.

Cost to Implementors:

None.

Cost to Users:

None.

Cost of Non-Adoption:

User confusion. Malformed Lisp code when an editor has removed a space at end of line.

Benefits:

Aesthetics:

Discussion:

• Bruno Haible says: ANSI CL 2.1.3 and the Glossary define Space to be a graphic character. (This is unlike ISO C 99, where space is non-graphic but printable.) I'm against introducing an additional category "printable character", because that complicates the standard. I agree that 22.1.3.2 should treat the space character differently.

• Kalle Olavi Niemitalo says: There already is a category of "printing" characters, according to the Glossary.

• pinterface says: CL does define the concept of standardized character names, of which #\Space is the only graphic character present. Rather than defining a new class of character or treating #\Space specially, would it not be enough to prefer the standardized name for any graphic character which has one? (That said, #\Space is often mentioned specially in the spec's discussions of characters, what's once more?)