{ $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." }
{ $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." }
{ $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." }
{ $description "Decomposes a tuple of type " { $snippet "class" } " into its component slot values by order of arguments. The inverse of " { $link boa } "." } ;
HELP:variant-class
{ $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 } "." } ;
{ POSTPONE:VARIANT: variant-class match } related-words
ARTICLE: "variants""Algebraic data types"
"The " { $vocab-link "variants" } " vocabulary provides syntax and combinators for defining and manipulating algebraic data types."