44 lines
1.3 KiB
Factor
44 lines
1.3 KiB
Factor
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! Copyright (c) 2012 Anonymous
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! See http://factorcode.org/license.txt for BSD license.
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USING: backtrack continuations kernel prettyprint sequences ;
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IN: rosetta-code.amb
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! http://rosettacode.org/wiki/Amb
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! Define and give an example of the Amb operator.
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! The Amb operator takes some number of expressions (or values
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! if that's simpler in the language) and nondeterministically
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! yields the one or fails if given no parameter, amb returns the
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! value that doesn't lead to failure.
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! The example is using amb to choose four words from the following strings:
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! set 1: "the" "that" "a"
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! set 2: "frog" "elephant" "thing"
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! set 3: "walked" "treaded" "grows"
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! set 4: "slowly" "quickly"
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! It is a failure if the last character of word 1 is not equal
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! to the first character of word 2, and similarly with word 2 and
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! word 3, as well as word 3 and word 4. (the only successful
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! sentence is "that thing grows slowly").
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CONSTANT: words {
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{ "the" "that" "a" }
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{ "frog" "elephant" "thing" }
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{ "walked" "treaded" "grows" }
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{ "slowly" "quickly" }
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}
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: letters-match? ( str1 str2 -- ? ) [ last ] [ first ] bi* = ;
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: sentence-match? ( seq -- ? ) dup rest [ letters-match? ] 2all? ;
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: select ( seq -- seq' ) [ amb-lazy ] map ;
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: search ( -- )
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words select dup sentence-match? [ " " join ] [ fail ] if . ;
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MAIN: search
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