Keyword read syntax would have more uses than just for keyword arguments so it would be great if such a thing would be added to R7RS-large: "syntax-rules" macros match identifiers hygienically (and not the underlying symbols using "eq?"/"equal?"). Sometimes, however, we want something that is matched using "equal?". At the moment, we can only use strings and numbers (and booleans and chars) in "syntax-rules" macros for that. For example, take a look at SRFI 165's "define-computation-type" and especially the definition of "clause" there. There, I am using the string "immutable" as a marker in the syntax, while an identifier named immutable might have been more natural. Then, however, I would have had to bind the identifier "immutable" and export it by SRFI 165. Now, keywords would be matched using "eq?"/"equal?" by "syntax-rules" macros. Thus, I could have simply used the keyword "immutable:" (or ":immutable" or "#'immutable" instead of the string "immutable" in SRFI 165, which would have looked much nicer) if keywords were available. Another use case is the definition of record types (especially in the context of inheritance): (define-record-type <rtd> (make-record field1) (field1 getter setter)) Record field names like "field1" are matched hygienically as identifiers in SRFI 150 and in R7RS-small (at least, this seems to have been intended by WG1) and this has quite a number of advantages, but when it comes to inheriting such records across libraries, it may be more convenient if these record file names do not have to be ex- and imported. Thus SRFI 150 allows to use strings instead (ugly!) but proposes to use keywords (nicer!) when they are available when non-hygienic matching is wanted: (define-record-type <rtd> (make-record field1:) (field1: getter setter)). ~~~~ If we don't want to use (or cannot use) the prefix "#'" for keywords, I would suggest adding SRFI 88 to R7RS-large. By default, the reader would read "foo:" as an identifier (to preserve compatibility to R7RS-small), but a reader flag to be introduced would switch the reader to read "foo:" as the keyword "foo:" (whose stringified name is "foo"). Furthermore "|foo:|" would be read as a symbol, "|foo|:" as a keyword. Thus, every Scheme port would get a flag (much like the case-folding flag) that can be enabled to support keywords. When enabled on output ports, keywords can be written. Symbols ending with ":" would be written using the "|...|" syntax. An extension of the port API would allow to get and set the case-folding and other flags on ports programmatically. -- Marc Am So., 3. Nov. 2019 um 23:34 Uhr schrieb Lassi Kortela <xxxxxx@lassi.io>: > > > I don't know. All lexical syntax ideas are on a separate docket so that > > people can fix their read implementations (which can be very complex) once > > and only once rather than piecemeal. > > If R7RS-large gets keyword read syntax, then it can in principle omit > the SRFI 177 hack of treating `foo:` and `:foo` symbols as keywords. -- Prof. Dr. Marc Nieper-Wißkirchen Universität Augsburg Institut für Mathematik Universitätsstraße 14 86159 Augsburg Tel: 0821/598-2146 Fax: 0821/598-2090 E-Mail: xxxxxx@math.uni-augsburg.de Web: www.math.uni-augsburg.de/alg/mitarbeiter/mnieper/
