D'OH. Sorry, I've been reading Common Lisp specs for so long that I read [ x y ] as "and optionally x followed by y", not "a list of x and y". I.e., I don't internally grok square brackets as parentheses. That makes the definition of the define syntax in
http://docs.racket-lang.org/reference/define.html arg = arg-id | [arg-id default-expr] | keyword arg-id | keyword [arg-id default-expr] much clearer. Thanks, and sorry for the noise! On Mon, Jun 23, 2014 at 9:29 AM, Tony Garnock-Jones <to...@ccs.neu.edu> wrote: > On 06/23/2014 09:21 AM, Joshua TAYLOR wrote: >>> (define y 2) >>> (define (f (x y)) >> (print x) >> (print y)) >> >> Is this expected? > > You've stumbled across Racket's syntax for default values for arguments, > a.k.a. optional arguments. [1] > > If I write > > (define (myproc [x "hello"]) ...) > > then if I call myproc with one argument, then x takes the value of that > argument, and if I call myproc with no arguments, then x takes its > default -- "hello". > > Your function, > > (define (f [x y]) ...) > > says "if x is omitted at the call site, then bind x to the value of the > variable y for the body of f". > > Regards, > Tony > > [1] > http://docs.racket-lang.org/guide/contracts-general-functions.html?q=optional#%28part._contracts-optional%29 -- Joshua Taylor, http://www.cs.rpi.edu/~tayloj/ ____________________ Racket Users list: http://lists.racket-lang.org/users
