187 lines
8.8 KiB
Factor
187 lines
8.8 KiB
Factor
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USING: help.markup help.syntax kernel kernel.private
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sequences words namespaces.private quotations vectors
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math.parser math ;
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IN: namespaces
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ARTICLE: "namespaces-combinators" "Namespace combinators"
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{ $subsection make-assoc }
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{ $subsection with-scope }
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{ $subsection with-variable }
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{ $subsection bind } ;
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ARTICLE: "namespaces-change" "Changing variable values"
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{ $subsection on }
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{ $subsection off }
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{ $subsection inc }
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{ $subsection dec }
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{ $subsection change } ;
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ARTICLE: "namespaces-global" "Global variables"
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{ $subsection namespace }
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{ $subsection global }
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{ $subsection get-global }
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{ $subsection set-global } ;
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ARTICLE: "namespaces-make" "Constructing sequences"
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"There is a lexicon of words for constructing sequences without passing the partial sequence being built on the stack. This reduces stack noise."
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{ $subsection make }
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{ $subsection , }
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{ $subsection % }
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{ $subsection # } ;
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ARTICLE: "namespaces.private" "Namespace implementation details"
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"The namestack holds namespaces."
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{ $subsection namestack }
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{ $subsection set-namestack }
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{ $subsection namespace }
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"A pair of words push and pop namespaces on the namestack."
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{ $subsection >n }
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{ $subsection ndrop } ;
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ARTICLE: "namespaces" "Variables and namespaces"
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"The " { $vocab-link "namespaces" } " vocabulary implements simple dynamically-scoped variables."
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$nl
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"A variable is an entry in an assoc of bindings, where the assoc is implicit rather than passed on the stack. These assocs are termed " { $emphasis "namespaces" } ". Nesting of scopes is implemented with a search order on namespaces, defined by a " { $emphasis "namestack" } ". Since namespaces are just assoc, any object can be used as a variable, however by convention, variables are keyed by symbols (see " { $link "symbols" } ")."
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$nl
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"The " { $link get } " and " { $link set } " words read and write variable values. The " { $link get } " word searches up the chain of nested namespaces, while " { $link set } " always sets variable values in the current namespace only. Namespaces are dynamically scoped; when a quotation is called from a nested scope, any words called by the quotation also execute in that scope."
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{ $subsection get }
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{ $subsection set }
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"Various utility words abstract away common variable access patterns:"
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{ $subsection "namespaces-change" }
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{ $subsection "namespaces-combinators" }
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{ $subsection "namespaces-global" }
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"A useful facility for constructing sequences by holding an accumulator sequence in a variable:"
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{ $subsection "namespaces-make" }
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"Implementation details your code probably does not care about:"
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{ $subsection "namespaces.private" }
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"An alternative to dynamic scope is lexical scope. Lexically-scoped values and closures are implemented in the " { $vocab-link "locals" } " vocabulary." ;
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ABOUT: "namespaces"
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HELP: get
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{ $values { "variable" "a variable, by convention a symbol" } { "value" "the value, or " { $link f } } }
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{ $description "Searches the name stack for a namespace containing the variable, and outputs the associated value. If no such namespace is found, outputs " { $link f } "." } ;
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HELP: set
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{ $values { "value" "the new value" } { "variable" "a variable, by convention a symbol" } }
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{ $description "Assigns a value to the variable in the namespace at the top of the name stack." }
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{ $side-effects "variable" } ;
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HELP: off
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{ $values { "variable" "a variable, by convention a symbol" } }
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{ $description "Assigns a value of " { $link f } " to the variable." }
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{ $side-effects "variable" } ;
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HELP: on
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{ $values { "variable" "a variable, by convention a symbol" } }
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{ $description "Assigns a value of " { $link t } " to the variable." }
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{ $side-effects "variable" } ;
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HELP: change
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{ $values { "variable" "a variable, by convention a symbol" } { "quot" "a quotation with stack effect " { $snippet "( old -- new )" } } }
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{ $description "Applies the quotation to the old value of the variable, and assigns the resulting value to the variable." }
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{ $side-effects "variable" } ;
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HELP: +@
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{ $values { "n" "a number" } { "variable" "a variable, by convention a symbol" } }
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{ $description "Adds " { $snippet "n" } " to the value of the variable. A variable value of " { $link f } " is interpreted as being zero." }
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{ $side-effects "variable" }
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{ $examples
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{ $example "SYMBOL: foo\n1 foo +@\n10 foo +@\nfoo get ." "11" }
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} ;
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HELP: inc
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{ $values { "variable" "a variable, by convention a symbol" } }
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{ $description "Increments the value of the variable by 1. A variable value of " { $link f } " is interpreted as being zero." }
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{ $side-effects "variable" } ;
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HELP: dec
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{ $values { "variable" "a variable, by convention a symbol" } }
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{ $description "Decrements the value of the variable by 1. A variable value of " { $link f } " is interpreted as being zero." }
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{ $side-effects "variable" } ;
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HELP: counter
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{ $values { "variable" "a variable, by convention a symbol" } { "n" integer } }
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{ $description "Increments the value of the variable by 1, and returns its new value." }
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{ $notes "This word is useful for generating (somewhat) unique identifiers. For example, the " { $link gensym } " word uses it." }
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{ $side-effects "variable" } ;
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HELP: with-scope
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{ $values { "quot" quotation } }
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{ $description "Calls the quotation in a new namespace. Any variables set by the quotation are discarded when it returns." } ;
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HELP: with-variable
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{ $values { "value" object } { "key" "a variable, by convention a symbol" } { "quot" quotation } }
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{ $description "Calls the quotation in a new namespace where " { $snippet "key" } " is set to " { $snippet "value" } "." }
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{ $examples "The following two phrases are equivalent:"
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{ $code "[ 3 x set foo ] with-scope" }
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{ $code "3 x [ foo ] with-variable" }
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} ;
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HELP: make-assoc
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{ $values { "quot" quotation } { "exemplar" "an assoc" } { "hash" "a new hashtable" } }
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{ $description "Calls the quotation in a new namespace of the same type as " { $snippet "exemplar" } ", and outputs this namespace when the quotation returns. Useful for quickly building assocs." } ;
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HELP: bind
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{ $values { "ns" "a hashtable" } { "quot" quotation } }
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{ $description "Calls the quotation in the dynamic scope of " { $snippet "ns" } ". When variables are looked up by the quotation, " { $snippet "ns" } " is checked first, and setting variables in the quotation stores them in " { $snippet "ns" } "." } ;
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HELP: namespace
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{ $values { "namespace" "an assoc" } }
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{ $description "Outputs the current namespace. Calls to " { $link set } " modify this namespace." } ;
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HELP: global
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{ $values { "g" "an assoc" } }
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{ $description "Outputs the global namespace. The global namespace is always checked last when looking up variable values." } ;
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HELP: get-global
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{ $values { "variable" "a variable, by convention a symbol" } { "value" "the value" } }
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{ $description "Outputs the value of a variable in the global namespace." } ;
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HELP: set-global
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{ $values { "value" "the new value" } { "variable" "a variable, by convention a symbol" } }
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{ $description "Assigns a value to the variable in the global namespace." }
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{ $side-effects "variable" } ;
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HELP: namestack*
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{ $values { "namestack" "a vector of assocs" } }
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{ $description "Outputs the current name stack." } ;
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HELP: namestack
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{ $values { "namestack" "a vector of assocs" } }
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{ $description "Outputs a copy of the current name stack." } ;
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HELP: set-namestack
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{ $values { "namestack" "a vector of assocs" } }
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{ $description "Replaces the name stack with a copy of the given vector." } ;
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HELP: >n
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{ $values { "namespace" "an assoc" } }
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{ $description "Pushes a namespace on the name stack." } ;
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HELP: ndrop
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{ $description "Pops a namespace from the name stack." } ;
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HELP: building
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{ $var-description "Temporary mutable growable sequence holding elements accumulated so far by " { $link make } "." } ;
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HELP: make
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{ $values { "quot" quotation } { "exemplar" "a sequence" } { "seq" "a new sequence" } }
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{ $description "Calls the quotation in a new " { $emphasis "dynamic scope" } ". The quotation and any words it calls can execute the " { $link , } " and " { $link % } " words to accumulate elements. When the quotation returns, all accumulated elements are collected into a sequence with the same type as " { $snippet "exemplar" } "." }
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{ $examples { $example "[ 1 , 2 , 3 , ] { } make ." "{ 1 2 3 }" } } ;
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HELP: ,
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{ $values { "elt" object } }
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{ $description "Adds an element to the end of the sequence being constructed by " { $link make } "." } ;
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HELP: %
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{ $values { "seq" "a sequence" } }
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{ $description "Appends a sequence to the end of the sequence being constructed by " { $link make } "." } ;
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HELP: init-namespaces
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{ $description "Resets the name stack to its initial state, holding a single copy of the global namespace. This word is called during startup and is rarely useful, except in certain situations such as the example below." }
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{ $examples
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"You can use this word to spawn a new thread which does not inherit the parent thread's dynamic variable bindings:"
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{ $code "[ init-namestack do-some-work ] in-thread" }
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} ;
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