Howdy Peter, ELan:
You're all talking about passing along refinements to
other functions. There will be a pretty easy way to do
it using COMPOSE:
NOTE -- This won't work on your REBOL yet!!! The
behavior of COMPOSE has been recently modified to throw
away UNSETs from PARENs. This change will be in the
next upcoming release.
(Right now, COMPOSE [()] == [unset], but this has
been changed so COMPOSE [()] = [])
SO, Given:
g: func [/a/b][
all [a print "A"]
all [b print "B"]
]
You can pass along refinements to g like this:
f: func [/a/b][
do to-path COMPOSE [g (either a ['a][]) (either b ['b][])]
]
or ...
h: func [/a/b][
foreach i [a b][either none? i [unset i][set i to-lit-word i]]
do to-path COMPOSE [g (a) (b)]
]
Not so bad a way to propagate refinements. The second
method would probably be more convenient for longer
sets of refinements. Of course, you can assemble the
to-path block to COMPOSE using, what else, COMPOSE!
On a related note, ( note: the rest of my rant on
COMPOSE is fully compliant with the current behavior
of COMPOSE) ... COMPOSE effectively provides Curried
functions. For instance, given:
f: func [parm1 parm2 parm3 parm4][do-something]
I just want to fill in parm4 and use defaults for
the others:
loop 1 COMPOSE [f 1 2 3 (some-computed-value)]
Here's another cool use of COMPOSE. You can create
local variables very easily:
vars: [a b c d e f g h i j k]
g: func COMPOSE [/local (vars)][ do-something ]
Lets say you have some functions that are very alike
but only different in a few spots. You can COMPOSE the
specs and the body and just evaluate sections that are
different:
foreach [name op] [my-add + my-sub -][
set name func [a b] compose [a (op) b]
]
That's a very simple example of what you could do.
You can use COMPOSE to generate PARSE rules!
Often you see people joining strings of code and DOing
them. That effectively turns REBOL into TCL, where
everything is just a string. That's inefficient and
sloppy. REBOL has great symbolic datatypes and
meta-abilities, and COMPOSE gives you the ability to
slice and dice REBOL expressions directly! This makes
for great leverage and power.
Just a rant on the marvels of COMPOSE...
-jeff
