Am Sa., 19. Okt. 2019 um 20:43 Uhr schrieb Shiro Kawai <xxxxxx@gmail.com>: > > On Sat, Oct 19, 2019 at 2:22 AM Marc Nieper-Wißkirchen <xxxxxx@nieper-wisskirchen.de> wrote: >> >> Hygiene is also a concern when identifiers are used as markers. This >> happens when they are record field names in record-type definitions. >> It also when they are used as keywords in `syntax-rules' macros (i.e. >> when they occur in the list of identifiers that are to be matched >> literally in `syntax-rules'). For example, `else' and `=>' are bound >> to some syntactic value by `(scheme base)', and when the transformer >> associated to `cond' expands such a `cond' form, it checks against the >> binding and not the name (see the definition of `free-identifier=?' in >> the R6RS). > > > These instances are reasonable and I'm not opposing it at all. I just think keywords are different. > Actually, keyword argument markers don't even need to be symbols or identifiers; they can be any > literal data, as far as they can be compared both at compile time and runtime (preferably, by eq?). > Runtime comparison is necessary, since keyword-value list can be (and need to be) passed around > via rest arguments. > > What do you say about necessity of renaming conflicting keywords from different libraries? Or > am I missing something and worring nonexistent problem? Think of a procedure `loggable' on may want to implement with keyword arguments. `loggable' shall take a procedure `f' and return a new procedure `g', which shall have the same interface as `f' except that `g' takes an extra keyword argument, say `logger:'. When `g' is called without the `logger:' argument, it shall foward the call to `f''. However, when the `logger.' argument is provided, `g' shall log to this logger that it is calling `f' before it is doing the actual call. As `f' may already be a procedure taking keyword arguments, it is here where hygiene is helpful because the symbol (!) `logger:' may clash with an already existing argument to `f'. Scheme is not CL and has hygienic macros. Its keyword-system shouldn't be less elegant and beautiful than its `syntax-rules' system.
