[r6rs-discuss] [Formal] Cleaning up make-transcoder's friends

---
This message is a formal comment which was submitted to formal-comment_at_r6rs.org, following the requirements described at: http://www.r6rs.org/process.html
---
Submitter: John Cowan
Email address: cowan_at_ccil.org
Issue type: Defect
Priority: Minor
Component: I/O
Report version: 5.91
Summary:  Clean up make-transcoder to accept three symbol arguments.
The current design of make-transcoder (Section 15.3.3, pp. 86-87)
involves passing it up to three arguments:
1) The first argument specifies the encoding, and is an object of unknown
type (OUT) which is either:
	a) the result of calling one of the standard *-code procedures; or
	b) obtained by an implementation-specific method.
2) The second argument specifies the EOL style.  It is either:
	a) one of the symbols 'cr, 'lf, 'crlf, or 'ls; or
	b) an OUT returned by the standard macro eol-style when passed
	an identifier other than one of those four; or
	c) an OUT returned by the standard procedure native-eol-style; or
	d) an OUT obtained by an implementation-specific method.
3) The third argument specifies the error handling mode.  It is either:
	a) one of the symbols 'ignore, 'raise, or 'replace; or
	b) an OUT returned by the standard macro error-handling-mode
	when passed an identifier other than one of those three; or
	c) an OUT obtained by an implementation-specific method.
In addition, if the third argument is omitted, it is the same as passing
'raise; if the second and third arguments are omitted, it is the same
as passing (native-eol-style) and 'raise respectively.
I can see absolutely no benefit to this diversity of interface styles.
I propose that make-transcoder take exactly three arguments which must
be symbols:
1) If the first argument is 'latin-1 or 'utf-8 or 'utf-16 or 'local, the
transcoder will use the specified character sets.  If it is a different
symbol, the meaning is implementation-defined.
2) If the first argument is 'cr or 'lf or 'crlf or 'universal, the
transcoder will use the specified EOL style, where 'universal means
"accept any EOL style on input, produce the local EOL style on output".
(For reference, the known EOL styles are CR, CR+LF, LF, NEL, CR+NEL, and
LS, where NEL = U+0085 and LS = U+2028.)  If it is a different symbol,
the meaning is implementation-defined.
3) If the third argument is 'ignore or 'raise or 'replace, then the
transcoder will take the appropriate action on encoding errors.  If it
is a different symbol, the meaning is implementation-defined.
-- 
Winter:  MIT,                                   John Cowan
Keio, INRIA,                                    cowan_at_ccil.org
Issue lots of Drafts.                           http://www.ccil.org/~cowan
So much more to understand!
Might simplicity return?                        (A "tanka", or extended haiku)