Hello Rebols:
I've got a question:
I've written a function called 'fetch, which has print
stubs to help follow the flow control.
If you evaluate 'print with 'fetch, no value is
returned.
Can someone tell me why this is so?
TIA
tim
(example and code follows)
Example:
>> do %test-fetch.r
Script: "Untitled" (none)
>> fetch 'abc
type = 'word
val is unset
returning unset words as default value
== none
>> fetch 'print
type = 'word
val is set
The code for 'fetch and helper function 'safe-reduce
follows:
REBOL[]
; -------------------------------------------------------------------------------
make object! [
default-value: none
set 'fetch func[ {safe data retrieval. Handles any value}
val [any-type!]
/seed {set default value} /deep {If block, reduce}
/same {If unset return 'val}
/local tmp][
either word? val[
print "type = 'word"
either value? val[
print "val is set"
get val
][
print "val is unset"
either same[
print "returning unset word as the word"
val
][
print "returning unset words as default value"
default-value
]
]
][ ; any other type but 'word
print ["type = " (type? val)]
either block? val[
either deep[
safe-reduce/deep val
][
safe-reduce val
]
][
val
]
]
]
]
; -------------------------------------------------------------------------------
safe-reduce: function[blk[block!] {reduce block, leaving unset values}
/deep {reduce nested blocks} ][rblk _reduce][
dummy: func[val /deep][val] ; pass
; below a function assignment using the prefix colon
_reduce: either deep[:safe-reduce][:dummy]
; since 'reduce is a native value (compiled into binary)
; try it first
either all[(not deep) (rblk: attempt[reduce blk])][
print "Used native 'reduce"
rblk
][
print "Block with unset values, using 'safe-reduce"
rblk: make block! length? blk
foreach element blk[
either word? element[
either value? element[
append rblk (get element)
][
append rblk element
]
][
either block? element[
append/only rblk _reduce/deep element
][
append rblk element
]
]
]
rblk
]
]
--
Tim Johnson <[EMAIL PROTECTED]>
http://www.alaska-internet-solutions.com
--
To unsubscribe from this list, just send an email to
[EMAIL PROTECTED] with unsubscribe as the subject.
