Dr. J. J. "One Eyed CrackerJack" Harbaugh -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Tim Johnson Sent: Friday, November 28, 2003 6:36 PM To: [EMAIL PROTECTED] Subject: [REBOL] Re: No return Value??? * Elan <[EMAIL PROTECTED]> [031128 13:42]: > Hi Tim. > > 1. You can use unset? to check for words that do not return values . > >> unset? print "" Thanks for reminding me. > == true > >> if unset? print "" [result: "<<unset>>"] > > 2. If you need to assign the return value of the tested function to > some > local word, you can use set/any to avoid an error. > > 3. Why doesn't print return a value? Wel;l, I suspect that is because > the purpose of print is to display its argument. If print were to return > a value, it would not only be displaying its argument, it would force > the REBOL interpreter to display print's return value as well. I.e. you > would see a combination of the printed argument and print's return value > on the screen. Instead of > >> print "" > > >> > > which is the expected result, for instance, you would get > > >> print_with_return: func [arg] [ print arg return true ] >> > print_with_return "" > > == true > >> > > BUT the argument to print was NOT "==true" it was "". > > Hope this helps. > > Elan > > > Tim Johnson wrote: > > >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 > > ] > > ] > > > > > > > > -- > To unsubscribe from this list, just send an email to > [EMAIL PROTECTED] with unsubscribe as the subject. -- 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. -- To unsubscribe from this list, just send an email to [EMAIL PROTECTED] with unsubscribe as the subject.
