70 lines
3.1 KiB
Factor
70 lines
3.1 KiB
Factor
USING: generic help.markup help.syntax sequences math
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math.parser ;
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IN: generic.standard
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HELP: no-method
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{ $values { "object" "an object" } { "generic" "a generic word" } }
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{ $description "Throws a " { $link no-method } " error." }
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{ $error-description "Thrown by the " { $snippet "generic" } " word to indicate it does not have a method for the class of " { $snippet "object" } "." } ;
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HELP: standard-combination
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{ $class-description
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"Performs standard method combination."
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$nl
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"Generic words using the standard method combination dispatch on the class of the object at the given stack position, where 0 is the top of the stack, 1 is the object underneath, and 2 is the next one under that. A " { $link no-method } " error is thrown if no suitable method is defined on the class."
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}
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{ $examples
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"A generic word for append strings and characters to a sequence, dispatching on the object underneath the top of the stack:"
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{ $code
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"G: build-string 1 standard-combination ;"
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"M: string build-string swap push-all ;"
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"M: integer build-string push ;"
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}
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} ;
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HELP: hook-combination
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{ $class-description
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"Performs hook method combination . See " { $link POSTPONE: HOOK: } "."
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} ;
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HELP: define-simple-generic
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{ $values { "word" "a word" } }
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{ $description "Defines a generic word with the " { $link standard-combination } " method combination and a dispatch position of 0." } ;
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{ standard-combination hook-combination } related-words
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HELP: no-next-method
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{ $error-description "Thrown by " { $link POSTPONE: call-next-method } " if the current method is already the least specific method." }
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{ $examples
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"The following code throws this error:"
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{ $code
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"GENERIC: error-test ( object -- )"
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""
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"M: number error-test 3 + call-next-method ;"
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""
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"M: integer error-test recip call-next-method ;"
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""
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"123 error-test"
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}
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"This results in the method on " { $link integer } " being called, which then calls the method on " { $link number } ". The latter then calls " { $link POSTPONE: call-next-method } ", however there is no method less specific than the method on " { $link number } " and so an error is thrown."
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} ;
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HELP: inconsistent-next-method
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{ $error-description "Thrown by " { $link POSTPONE: call-next-method } " if the values on the stack are not compatible with the current method." }
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{ $examples
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"The following code throws this error:"
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{ $code
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"GENERIC: error-test ( object -- )"
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""
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"M: string error-test print ;"
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""
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"M: integer error-test number>string call-next-method ;"
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""
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"123 error-test"
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}
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"This results in the method on " { $link integer } " being called, which then passes a string to " { $link POSTPONE: call-next-method } ". However, this fails because the string is not compatible with the current method."
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$nl
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"This usually indicates programmer error; if the intention above was to call the string method on the result of " { $link number>string } ", the code should be rewritten as follows:"
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{ $code "M: integer error-test number>string error-test ;" }
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} ;
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