text: ! Copyright (C) 2009 Joe Groff.
  ! See http://factorcode.org/license.txt for BSD license.
  USING: classes.mixin help.markup help.syntax kernel multiline roles ;
  IN: roles
  
  HELP: ROLE:
  { $syntax "ROLE: name slots... ;
  ROLE: name < role slots... ;
  ROLE: name <{ roles... } slots... ;" }
  { $description "Defines a new " { $link role } ". " { $link tuple } " classes which inherit this role will contain the specified " { $snippet "slots" } " as well as the slots associated with the optional inherited " { $snippet "roles" } "."
  $nl
  "Slot specifiers take one of the following three forms:"
  { $list
      { { $snippet "name" } " - a slot which can hold any object, with no attributes" }
      { { $snippet "{ name attributes... }" } " - a slot which can hold any object, with optional attributes" }
      { { $snippet "{ name class attributes... }" } " - a slot specialized to a specific class, with optional attributes" }
  }
  "Slot attributes are lists of slot attribute specifiers followed by values; a slot attribute specifier is one of " { $link initial: } " or " { $link read-only } ". See " { $link "tuple-declarations" } " for details." } ;
  
  HELP: ROLE-TUPLE:
  { $syntax "ROLE-TUPLE: name slots ;
  ROLE-TUPLE: name < estate slots ;
  ROLE-TUPLE: name <{ estates... } slots... ;" }
  { $description "Defines a new " { $link tuple } " class."
  $nl
  "The list of inherited " { $snippet "estates" } " is optional; a single tuple superclass and/or a set of " { $link role } "s can be specified. If no superclass is provided, it defaults to " { $link tuple } "."
  $nl
  "Slot specifiers take one of the following three forms:"
  { $list
      { { $snippet "name" } " - a slot which can hold any object, with no attributes" }
      { { $snippet "{ name attributes... }" } " - a slot which can hold any object, with optional attributes" }
      { { $snippet "{ name class attributes... }" } " - a slot specialized to a specific class, with optional attributes" }
  }
  "Slot attributes are lists of slot attribute specifiers followed by values; a slot attribute specifier is one of " { $link initial: } " or " { $link read-only } ". See " { $link "tuple-declarations" } " for details." } ;
  
  {
      POSTPONE: ROLE:
      POSTPONE: ROLE-TUPLE:
  } related-words
  
  HELP: role
  { $class-description "The superclass of all role classes. A " { $snippet "role" } " is a " { $link mixin-class } " that includes a set of slot definitions that can be added to " { $link tuple } " classes alongside other " { $snippet "role" } "s." } ;
  
  HELP: multiple-inheritance-attempted
  { $class-description "This error is thrown if a " { $link POSTPONE: ROLE-TUPLE: } " definition attempts to inherit more than one " { $link tuple } " class." } ;
  
  HELP: role-slot-overlap
  { $class-description "This error is thrown if a " { $link POSTPONE: ROLE-TUPLE: } " or " { $link POSTPONE: ROLE: } " definition attempts to inherit a set of " { $link role } "s in which more than one attempts to define the same slot." } ;
  
  ARTICLE: "roles" "Roles"
  "The " { $vocab-link "roles" } " vocabulary provides a form of tuple interface that can be implemented by concrete tuple classes. A " { $link role } " definition is a mixin class that also prescribes a set of tuple slots. Roles are not tuple classes by themselves and cannot be instantiated by " { $link new } ". The vocabulary extends " { $link POSTPONE: ROLE-TUPLE: } " syntax to allow concrete tuple types to declare membership to one or more roles, automatically including their prescribed slots." $nl
  "The role superclass:"
  { $subsections role }
  "Syntax for making a new role:"
  { $subsection POSTPONE: ROLE: }
  "Syntax for making tuples that use roles:"
  { $subsection POSTPONE: ROLE-TUPLE: }
  "Errors with roles:"
  { $subsections multiple-inheritance-attempted role-slot-overlap } ;
  
  ABOUT: "roles"
  