Chicanery: subtle, opinionated improvements to R7RS Scheme

While I was reading the R7RS specification, I was a little annoyed by how broken up the standard library seemed to be. While the most egregious example is maybe (scheme case-lambda), which exports … only case-lambda, the other libraries like (scheme write) for display, (scheme cxr) for functions like caddr but not cddr, and the rest didn’t really seem logical to me. Plus, in CHICKEN scheme, the one I usually use, utf8 is an egg you need to install separately…

To ameliorate these minor warts in what I otherwise consider to be an excellent language, chicanery was born. It’s kind of like a prelude, I suppose? It imports all r7rs modules and re-exports their identifiers, and makes sure the implementation is Unicode-aware. It also includes a few extras ;)

Chicanery extras

I also thought it was strange that map, for-each, and append apply to lists only, while vector-map and string-for-each, exist, for example. chicanery prefixes the default map, for-each, and append functions with list-, and redefines those identifiers to functions that are generic over Scheme’s base collection types (lists, strings, vectors, bytevectors where applicable). I didn’t make the functions fully-generic to keep them efficient and because I don’t know how to do that, but you can still use vector-append or list-map if you know what type you need and want speed.

In a similar vein, I’ve also added generic functions ref and copy that dispatch to string-ref, list-copy, and the like.

Other extras include

• (atom? x) determines whether x is an atom (i.e., not a pair or null)
• (read-port), (read-port port) reads a port until hitting end-of-file (IDK why this isn’t in R7RS!), in chunks of read-port-chunk-size
• (defined? x) returns whether the symbol x is bound to a variable
• (with-input-from-string str thunk) calls thunk with str bound as the current-input-port.
• (with-output-to-string thunk) calls thunk and returns a string of the output.
• (displayed x), (->string x) returns x as a string (via display)
• (written x) returns x as a string (via write)
• (print x ...) displays x ... followed by a newline

Supported Scheme implementations

chicanery now supports multiple R7RS implementations! The full list can be found by running make, but here’s what we have right now:

Chicken

Guile

Gambit

Other Scheme implementations have been minimally tested and I haven’t been able to figure them out yet. However, Cyclone is definitively not compatible; see issue #413.

License

This software is licensed under the GWL, v. 1.0. See COPYING for details.