Am Thu, 14 Jan 2010 23:17:04 -0800
schrieb Jim mack <[email protected]>:
> Hi. Can you please help me understand why the final line here
> results in a stack underflow?
>
> USING: accessors arrays kernel locals present select8.html
> classes.tuple sequences prettyprint fry macros nested-comments
> combinators ;
>
> TUPLE: testing id firstname lastname age ;
> : <testing> ( id fn ln age -- tpl ) testing boa ;
> : testdata ( -- tpl ) 1 "jim" "mack" 46 <testing> ;
> : testing-schema ( -- seq )
> { { "First Name " [ firstname>> ] }
> { "Last Name " [ lastname>> ] }
> { "Age " [ age>> ] } } ;
>
> : non-macro-way ( tpl -- )
> {
> [ "First Name " write firstname>> print ]
> [ "Last Name " write lastname>> print ]
> [ "Age " write age>> present print ]
> } cleave ;
>
> testdata non-macro-way
>
> ! using fry
>
> testdata { } clone
> testing-schema [ first2 '[ _ write @ present print ] suffix ] each
> cleave
>
> MACRO: easier ( alist -- ) { } clone swap
> [ first2 '[ _ write @ present print ] suffix ] each cleave ;
>
> : fancyprint ( tpl -- )
> testing-schema easier ; inline
>
> testdata fancyprint ! stack underflow
Hi Jim
If I understand you correctly, your intent is that fancyprint will be
the same as non-macro-way, just with dynamically generated code. If so,
your problem is that you don't generate a quotation as output of the
macro, specifically the call to cleave gets executed at parse time.
Here's a correct version (with { } clone swap [ .. suffix ] each
simplified to map):
MACRO: easier ( alist -- )
[ first2 '[ _ write @ present print ] ] map '[ _ cleave ] ;
For fancyprint to work, you have to declare testing-schema inline, make
a CONSTANT: out of it or directly write the alist into fancyprint.
Cheers
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