Mailing List Archive: 49091 messages
  • Home
  • Script library
  • AltME Archive
  • Mailing list
  • Articles Index
  • Site search

[REBOL] Re: [refactoring s-c?]

From: rebol665:ifrance at: 17-Mar-2002 22:16

Hi Ladislav, 1. first 'first If I understand nonsame1 is equivalent to nonsame except if called with the word 'first. <<yoda>> same? 'first nonsame1 'first ** Script Error: first has no value <<L>> So I have tried to find out the part of nonsame1 that breaks ... In the following line from nonsame1, I see two parts : use reduce [word] reduce ['first reduce [word]] or use <part 1> <part 2> <part 1> being a block of words, here a block with only one word. <part 2> being a block to evaluate. Evaluation returning the given word. A little test shows that <part 1> is correct.
>> myword: 'first
== first
>> reduce [myword]
== [first] Therefore I concentrate myself on <part 2>. To emulate <part 2> I create this little function test: func [x [word!]][do reduce ['first reduce [x]]] However I was desappointed with the result.
>> test myword
== first No error, so neither <part 1> or <part 2> is responsible for the error. It is only when they are bind together by use, that an error rises. I think also there is nothing wrong with 'first by itself. To clear that, I have made the following test where 'first is replaced by 'second.
>> test2: func [word [word!]][use reduce [word] reduce ['second reduce
>> test2 'second
** Script Error: second has no value Bingo ! let's try to remove first ...
>> test2: func [word [word!]][use reduce [word] reduce [reduce [word]]] >> test2 'first
== [first] It is almost ok, except that a block is returned instead of a word. And it was indeed the purpose of using 'first to give us a word. A part that it returns a block, test2 give us the right thing : a word with the same spelling but not the same word.
>> first test2 'first
== first Here we can get the "new" first with the same spelling.
>> same? 'first first test2 'first
== false And it is not the same as the global first. From that it is easy to build test3 which is indeed nonsame :
>> test3: func [word [word!]][first use reduce [word] reduce [reduce
>> test3 'first
== first
>> same? 'first test3 'first
== false 2. second reduce Let's play again with my simplification of use : use <part 1> <part 2> where <part 1> is a block including one word <part 2> is a block returning that word Why can't we simply write : test4: func [x [word!]][use [x][x]] This is an answer
>> use [x][x]
** Script Error: x has no value ** Where: do-boot ** Near: x The x in part 2 exists but have never been set. It has no value to return. In fact, we don't want the value of x but the word associated. May be this could work. test4: func [x [word!]][use [x]['x]]
>> test4 'first
== x Nope, 'x is taken litteraly here. test4: func [x [word!]][use [x][compose [('x)]]]
>> test4 'first
== [x] test4: func [x [word!]][use reduce [x][compose [('x)]]]
>> test 'first
== [first [first]] Yeah, another puzzle: one in -> two out. However it is first that comes out. So I think I understand the first reduce. Let's replace compose by reduce too. test4: func [x [word!]][use reduce [x][reduce [x]]]
>> test4 'first
== [first] Not bad ! but is it the real one ?
>> same? 'first first test4 'first
== true No luck again. Indeed it says something. Since we get the global 'first, it means that the use did not work at all. This one is a bit tricky test5: func [x [word!]][use [first][reduce [x]]]
>> test5 'first
== [first]
>> same? 'first test5 'first
== false It works, however it works only with 'first. It shows anyway that only <part 2> needs to be taken care of. Let's try to see what is wrong in that <part 2>. test6: func [x [word!]][use reduce [x][print reduce [x]]]
>> test6 'first
** Script Error: first expected series argument of type: series pair event money date object port time tuple any-function library struct event ** Where: test6 ** Near: first It seems that x is evaluated again. To prevent evaluation, it can be put in an extra block. test6: func [x [word!]][use reduce [x][print [reduce [x]]]]
>> test6 'first
first As we know that print reduces its argument, all we have to do is to replace print by reduce. test7: func [x [word!]][use reduce [x][reduce [reduce [x]]]]
>> test7 'first
== [[first]] And yet there is an external block to get rid of. test8: func [x [word!]][use reduce [x] reduce [reduce [x]]]
>> test8 'first
== [first]
>> same? 'first test8 'first
== false And finally from what we learned from (1.). test9: func [x [word!]][first use reduce [x] reduce [reduce [x]]]
>> test9 'first
== first
>> same? 'first test9 'first
== false Which is not a surprise because test9 is nonsame. 3. third contexts.html I was very proud to see my name in the acknowledgements part. I show it to everybody in the house except my cat. 4. fourth unbound I noticed the replacement of error? by any-type? I will look into later, because I have very few little grey cells available at the moment. Patrick