63 lines
1.4 KiB
Forth
63 lines
1.4 KiB
Forth
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From my mastodon feed:
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@millihertz@oldbytes.space:
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so i just saw this example given as a reason why
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concatenative languages tend to be called "write-only":
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f x y z = y² + x<EFBFBD>- |y|
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: f
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drop dup dup *
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swap abs
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rot3 dup *
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swap - + ;
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... snipped ...
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He ends up writing the following:
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lastly, nobody would ever write Forth like that anyway!
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: ²+ dup * swap dup * + ;
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: y²+x²-|y| ( y x -- result )
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tuck ²+ swap abs - ;
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Given a dislike of stack shufflers, a Retro implementation could be:
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:f [ [ n:square ] bi@ + ] sip n:abs - ;
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Assuming one knows the combinators, this is pretty straightforward,
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but doesn't really resemble the original formula. I decided to write
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a quick set of words to let me convert the original formula into
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something more recognizable while still being RPN.
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:f /xyz
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x: n:square y: n:square + y: n:abs - ;
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This adds a / sigil that maps stack values to an internal set of
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variables, whose values are returned by words with the variable names
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followed by a colon.
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The code follows.
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~~~
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'Vars d:create #256 allot
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'abcdefghijklmnopqrstuvwxyz s:keep
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[ dup ':%c:_&Vars_$%c_+_fetch_; s:format s:evaluate ] s:for-each
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:sigil:/
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s:reverse [ 'liliadst i , &Vars , ] s:for-each ; immediate
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~~~
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And the test case:
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```
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:f /xyz
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x: n:square y: n:square + y: n:abs - ;
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#33 #12 #301 f n:put
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```
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