67 lines
4.0 KiB
Factor
67 lines
4.0 KiB
Factor
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USING: help.markup help.syntax math strings words ;
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IN: effects
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ARTICLE: "effect-declaration" "Stack effect declaration"
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"It is good practice to declare the stack effects of words using the following syntax:"
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{ $code ": sq ( x -- y ) dup * ;" }
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"A stack effect declaration is written in parentheses and lists word inputs and outputs, separated by " { $snippet "--" } ". Stack effect declarations are read in using a parsing word:"
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{ $subsection POSTPONE: ( }
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"Stack elements in a stack effect are ordered so that the top of the stack is on the right side. Each value can be named by a data type or description. The following are some examples of value names:"
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{ $table
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{ { { $snippet "?" } } "a boolean" }
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{ { { $snippet "elt" } } "an object which is an element of a sequence" }
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{ { { $snippet "m" } ", " { $snippet "n" } } "an integer" }
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{ { { $snippet "obj" } } "an object" }
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{ { { $snippet "quot" } } "a quotation" }
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{ { { $snippet "seq" } } "a sequence" }
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{ { { $snippet "assoc" } } "an associative mapping" }
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{ { { $snippet "str" } } "a string" }
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{ { { $snippet "x" } ", " { $snippet "y" } ", " { $snippet "z" } } "a number" }
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{ { $snippet "loc" } "a screen location specified as a two-element array holding x and y co-ordinates" }
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{ { $snippet "dim" } "a screen dimension specified as a two-element array holding width and height values" }
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{ { $snippet "*" } "when this symbol appears by itself in the list of outputs, it means the word unconditionally throws an error" }
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}
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"The stack effect inferencer verifies stack effect comments to ensure the correct number of inputs and outputs is listed. Value names are ignored; only their number matters. An error is thrown if a word's declared stack effect does not match its inferred stack effect."
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$nl
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"Recursive words must declare a stack effect in order to compile. This includes all generic words, due to how delegation is implemented." ;
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ARTICLE: "effects" "Stack effects"
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"A " { $emphasis "stack effect declaration" } ", for example " { $snippet "( x y -- z )" } " denotes that an operation takes two inputs, with " { $snippet "y" } " at the top of the stack, and returns one output."
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$nl
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"Stack effects are first-class, and words for working with them are found in the " { $vocab-link "effects" } " vocabulary."
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{ $subsection effect }
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{ $subsection effect? }
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"Stack effects of words can be declared."
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{ $subsection "effect-declaration" }
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"Getting a word's declared stack effect:"
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{ $subsection stack-effect }
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"Converting a stack effect to a string form:"
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{ $subsection effect>string }
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"Comparing effects:"
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{ $subsection effect-height }
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{ $subsection effect<= } ;
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ABOUT: "effects"
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HELP: effect
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{ $class-description "An object representing a stack effect. Holds a sequence of inputs, a sequence of outputs and a flag indicating if an error is thrown unconditionally." } ;
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HELP: effect-height
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{ $values { "effect" effect } { "n" integer } }
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{ $description "Outputs the number of objects added to the data stack by the stack effect. This will be negative if the stack effect only removes objects from the stack." } ;
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HELP: effect<=
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{ $values { "eff1" effect } { "eff2" effect } { "?" "a boolean" } }
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{ $description "Tests if " { $snippet "eff1" } " is substitutable for " { $snippet "eff2" } ". What this means is that both stack effects change the stack height by the same amount, the first takes a smaller or equal number of inputs as the second, and either both or neither one terminate execution by throwing an error." } ;
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HELP: effect>string
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{ $values { "effect" effect } { "string" string } }
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{ $description "Turns a stack effect object into a string mnemonic." }
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{ $examples
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{ $example "USE: effects" "1 2 <effect> effect>string print" "( object -- object object )" }
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} ;
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HELP: stack-effect
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{ $values { "word" word } { "effect/f" "an " { $link effect } " or " { $link f } } }
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{ $description "Outputs the stack effect of a word; either a stack effect declared with " { $link POSTPONE: ( } ", or an inferred stack effect (see " { $link "inference" } "." } ;
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