94 lines
4.9 KiB
Factor
94 lines
4.9 KiB
Factor
USING: help.markup help.syntax words math source-files
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parser quotations compiler.units ;
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IN: definitions
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ARTICLE: "definition-protocol" "Definition protocol"
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"A common protocol is used to build generic tools for working with all definitions."
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$nl
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"Definitions must know what source file they were loaded from, and provide a way to set this:"
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{ $subsections
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where
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set-where
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}
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"Definitions can be removed:"
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{ $subsections forget }
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"Definitions must implement a few operations used for printing them in source form:"
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{ $subsections
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definer
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definition
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}
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{ $see-also "see" } ;
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ARTICLE: "definition-checking" "Definition sanity checking"
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"When a source file is reloaded, the parser compares the previous list of definitions with the current list; any definitions which are no longer present in the file are removed by a call to " { $link forget } ". A warning message is printed if any other definitions still depend on the removed definitions."
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$nl
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"The parser also catches forward references when reloading source files. This is best illustrated with an example. Suppose we load a source file " { $snippet "a.factor" } ":"
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{ $code
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"USING: io sequences ;"
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"IN: a"
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": hello \"Hello\" ;"
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": world \"world\" ;"
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": hello-world hello " " world 3append print ;"
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}
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"The definitions for " { $snippet "hello" } ", " { $snippet "world" } ", and " { $snippet "hello-world" } " are in the dictionary."
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$nl
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"Now, after some heavily editing and refactoring, the file looks like this:"
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{ $code
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"USING: namespaces ;"
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"IN: a"
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": hello \"Hello\" % ;"
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": hello-world [ hello " " % world ] \"\" make ;"
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": world \"world\" % ;"
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}
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"Note that the developer has made a mistake, placing the definition of " { $snippet "world" } " " { $emphasis "after" } " its usage in " { $snippet "hello-world" } "."
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$nl
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"If the parser did not have special checks for this case, then the modified source file would still load, because when the definition of " { $snippet "hello-world" } " on line 4 is being parsed, the " { $snippet "world" } " word is already present in the dictionary from an earlier run. The developer would then not discover this mistake until attempting to load the source file into a fresh image."
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$nl
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"Since this is undesirable, the parser explicitly raises a " { $link no-word } " error if a source file refers to a word which is in the dictionary, but defined after it is used."
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$nl
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"The parser also catches duplicate definitions. If an artifact is defined twice in the same source file, the earlier definition will never be accessible, and this is almost always a mistake, perhaps due to a bad choice of word names, or a copy and paste error. The parser raises an error in this case."
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{ $subsections redefine-error } ;
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ARTICLE: "definitions" "Definitions"
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"A " { $emphasis "definition" } " is an artifact read from a source file. Words for working with definitions are found in the " { $vocab-link "definitions" } " vocabulary."
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$nl
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"Definitions are defined using parsing words. Examples of definitions together with their defining parsing words are words (" { $link POSTPONE: : } "), methods (" { $link POSTPONE: M: } "), and vocabularies (" { $link POSTPONE: IN: } ")."
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$nl
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"All definitions share some common traits:"
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{ $list
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"There is a word to list all definitions of a given type"
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"There is a parsing word for creating new definitions"
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"There is an ordinary word which is the runtime equivalent of the parsing word, for introspection"
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"Instances of the definition may be introspected and modified with the definition protocol"
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}
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"For every source file loaded into the system, a list of definitions is maintained. Pathname objects implement the definition protocol, acting over the definitions their source files contain. See " { $link "source-files" } " for details."
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{ $subsections
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"definition-protocol"
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"definition-checking"
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"compilation-units"
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}
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"A parsing word to remove definitions:"
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{ $subsections POSTPONE: FORGET: }
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{ $see-also "see" "parser" "source-files" "words" "generic" "help-impl" } ;
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ABOUT: "definitions"
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HELP: where
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{ $values { "defspec" "a definition specifier" } { "loc" "a " { $snippet "{ path line# }" } " pair" } }
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{ $description "Outputs the location of a definition. If the location is not known, will output " { $link f } "." } ;
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HELP: set-where
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{ $values { "loc" "a " { $snippet "{ path line# }" } " pair" } { "defspec" "a definition specifier" } }
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{ $description "Sets the definition's location." }
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{ $notes "This word is used by the parser." } ;
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HELP: forget
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{ $values { "defspec" "a definition specifier" } }
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{ $description "Forgets about a definition. For example, if it is a word, it will be removed from its vocabulary." }
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{ $notes "This word must be called from inside " { $link with-compilation-unit } "." } ;
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HELP: forget-all
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{ $values { "definitions" "a sequence of definition specifiers" } }
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{ $description "Forgets every definition in a sequence." }
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{ $notes "This word must be called from inside " { $link with-compilation-unit } "." } ;
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