79 lines
3.1 KiB
Factor
79 lines
3.1 KiB
Factor
! (c)2009 Joe Groff bsd license
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USING: arrays classes classes.singleton classes.tuple help.markup
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help.syntax kernel multiline slots quotations ;
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IN: variants
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HELP: VARIANT:
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{ $syntax """
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VARIANT: class-name
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singleton
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singleton
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tuple: { slot slot slot ... }
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.
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.
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.
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; """ }
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{ $description "Defines " { $snippet "class-name" } " as a union of the following " { $link singleton-class } " and " { $link tuple-class } " definitions. Each " { $snippet "singleton" } " word is defined as a " { $snippet "singleton-class" } ", and each " { $snippet "tuple" } " word is defined as a " { $snippet "tuple-class" } " with the given set of " { $snippet "slot" } "s, using the same syntax for slot specifiers as " { $link POSTPONE: TUPLE: } ". Typed tuple slots can recursively reference the variant " { $snippet "class-name" } " being defined. For " { $snippet "tuple" } " types, a " { $link boa } " constructor word " { $snippet "<tuple>" } " is defined as well." }
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{ $examples { $code """
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USING: kernel variants ;
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IN: scratchpad
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VARIANT: list
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nil
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cons: { { first object } { rest list } }
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;
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""" } } ;
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HELP: VARIANT-MEMBER:
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{ $description "Defines a new member of a variant class without restricting such definitions to a single statement or source file. The variant class should be listed first, and the class member should follow." }
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{ $examples { $code """
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USING: kernel variants ;
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IN: scratchpad
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VARIANT: list ;
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VARIANT-MEMBER: list nil
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VARIANT-MEMBER: list cons: { { first object } { rest list } }
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""" } } ;
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HELP: match
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{ $values { "branches" array } }
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{ $description "Dispatches on the type of the value on the top of the stack. If the type is a " { $link singleton-class } ", the corresponding quotation is called with the underlying stack unchanged. If the type is a " { $link tuple-class } ", the tuple slots are pushed onto the stack by order of arguments." }
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{ $examples { $example """
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USING: kernel math prettyprint variants ;
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IN: scratchpad
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VARIANT: list
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nil
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cons: { { first object } { rest list } }
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;
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: list-length ( list -- length )
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{
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{ nil [ 0 ] }
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{ cons [ nip list-length 1 + ] }
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} match ;
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1 2 3 4 nil <cons> <cons> <cons> <cons> list-length .
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""" "4" } } ;
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HELP: unboa
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{ $values { "class" class } }
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{ $description "Decomposes a tuple of type " { $snippet "class" } " into its component slot values by order of arguments. The inverse of " { $link boa } "." } ;
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HELP: variant-class
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{ $class-description "This class comprises class names that have been defined with " { $link POSTPONE: VARIANT: } ". When a " { $snippet "variant-class" } " is used as the type of a specialized " { $link tuple } " slot, the variant's first member type is used as the default " { $link initial-value } "." } ;
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{ POSTPONE: VARIANT: variant-class match } related-words
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ARTICLE: "variants" "Algebraic data types"
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"The " { $vocab-link "variants" } " vocabulary provides syntax and combinators for defining and manipulating algebraic data types."
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{ $subsections
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POSTPONE: VARIANT:
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POSTPONE: VARIANT-MEMBER:
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variant-class
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match
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} ;
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ABOUT: "variants"
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