67 lines
4.0 KiB
Factor
67 lines
4.0 KiB
Factor
! Copyright (C) 2006 Chris Double.
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! See http://factorcode.org/license.txt for BSD license.
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USING: help.markup help.syntax namespaces assocs sequences
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kernel combinators ;
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IN: match
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HELP: match
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{ $values { "value1" object } { "value2" object } { "bindings" assoc }
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}
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{ $description "Pattern match " { $snippet "value1" } " against " { $snippet "value2" } ". These values can be any Factor value, including sequences and tuples. The values can contain pattern variables, which are symbols that begin with '?'. The result is a hashtable of the bindings, mapping the pattern variables from one sequence to the equivalent value in the other sequence. The " { $link _ } " symbol can be used to ignore the value at that point in the pattern for the match. " }
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{ $examples
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{ $unchecked-example "USE: match" "MATCH-VARS: ?a ?b ;\n{ ?a { 2 ?b } 5 } { 1 { 2 3 } _ } match ." "H{ { ?a 1 } { ?b 3 } }" }
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}
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{ $see-also match-cond POSTPONE: MATCH-VARS: replace-patterns match-replace } ;
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HELP: match-cond
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{ $values { "assoc" "a sequence of pairs" } }
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{ $description "Calls the second quotation in the first pair whose first sequence yields a successful " { $link match } " against the top of the stack. The second quotation, when called, has the hashtable returned from the " { $link match } " call bound as the top namespace so " { $link get } " can be used to retrieve the values. A single quotation will always yield a true value. To have a fallthrough match clause use the " { $link _ } " match variable." }
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{ $errors "Throws a " { $link no-match-cond } " error if none of the test quotations yield a true value." }
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{ $examples
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{ $code
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"USE: match" "MATCH-VARS: ?value ;\n{ increment 346126 } {\n { { increment ?value } [ ?value do-something ] }\n { { decrement ?value } [ ?value do-something-else ] }\n { _ [ no-match-found ] }\n} match-cond" }
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}
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{ $see-also match POSTPONE: MATCH-VARS: replace-patterns match-replace } ;
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HELP: MATCH-VARS:
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{ $syntax "MATCH-VARS: var ... ;" }
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{ $values { "var" "a match variable name beginning with '?'" } }
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{ $description "Creates a symbol that can be used in " { $link match } " and " { $link match-cond } " for binding values in the matched sequence. The symbol name is created as a word that is defined to get the value of the symbol out of the current namespace. This can be used in " { $link match-cond } " to retrive the values in the quotation body." }
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{ $examples
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{ $code "USE: match" "MATCH-VARS: ?value ;\n{ increment 346126 } {\n { { increment ?value } [ ?value do-something ] }\n { { decrement ?value } [ ?value do-something-else ] }\n { _ [ no-match-found ] }\n} match-cond" }
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}
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{ $see-also match match-cond replace-patterns match-replace } ;
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HELP: replace-patterns
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{ $values { "object" object } { "result" object } }
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{ $description "Copy the object, replacing each occurrence of a pattern matching variable with the actual value of that variable." }
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{ $see-also match-cond POSTPONE: MATCH-VARS: match-replace } ;
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HELP: match-replace
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{ $values { "object" object } { "pattern1" object } { "pattern2" object } { "result" object } }
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{ $description "Matches the " { $snippet "object" } " against " { $snippet "pattern1" } ". The pattern match variables in " { $snippet "pattern1" } " are assigned the values from the matching " { $snippet "object" } ". These are then replaced into the " { $snippet "pattern2" } " pattern match variables." }
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{ $examples
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{ $example
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"USING: match prettyprint ;"
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"IN: scratchpad"
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"MATCH-VARS: ?a ?b ;"
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"{ 1 2 } { ?a ?b } { ?b ?a } match-replace ."
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"{ 2 1 }"
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}
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}
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{ $see-also match-cond POSTPONE: MATCH-VARS: } ;
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ARTICLE: "match" "Pattern matching"
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"The " { $vocab-link "match" } " vocabulary implements ML-style pattern matching."
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$nl
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"Variables used for pattern matching must be explicitly defined first:"
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{ $subsections POSTPONE: MATCH-VARS: }
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"A basic pattern match:"
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{ $subsections match }
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"A conditional form analogous to " { $link cond } ":"
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{ $subsections match-cond }
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"Pattern replacement:"
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{ $subsections match-replace } ;
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ABOUT: "match"
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