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@ -21,7 +21,7 @@ $nl
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ARTICLE: "inference-combinators" "Combinator stack effects"
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"Without further information, one cannot say what the stack effect of " { $link call } " is; it depends on the given quotation. If the inferencer encounters a " { $link call } " without further information, a " { $link literal-expected } " error is raised."
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{ $example "[ dup call ] infer." "Literal value expected\n\nType :help for debugging help." }
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{ $example "[ dup call ] infer." "Got a computed value where a literal quotation was expected\n\nType :help for debugging help." }
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"On the other hand, the stack effect of applying " { $link call } " to a literal quotation or a " { $link curry } " of a literal quotation is easy to compute; it behaves as if the quotation was substituted at that point:"
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{ $example "[ [ 2 + ] call ] infer." "( object -- object )" }
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"Consider a combinator such as " { $link keep } ". The combinator itself does not have a stack effect, because it applies " { $link call } " to a potentially arbitrary quotation. However, since the combinator is declared " { $link POSTPONE: inline } ", a given usage of it can have a stack effect:"
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@ -38,7 +38,7 @@ $nl
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{ $example ": foo 0 [ + ] ; inline" "[ foo reduce ] infer." "( object -- object )" }
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"Passing a literal quotation on the data stack through an inlined recursive combinator nullifies its literal status. For example, the following will not infer:"
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{ $example
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"[ [ reverse ] swap [ reverse ] map swap call ] infer." "Literal value expected\n\nType :help for debugging help."
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"[ [ reverse ] swap [ reverse ] map swap call ] infer." "Got a computed value where a literal quotation was expected\n\nType :help for debugging help."
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}
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"To make this work, pass the quotation on the retain stack instead:"
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{ $example
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@ -67,11 +67,11 @@ $nl
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"If a recursive word takes quotation parameters from the stack and calls them, it must be declared " { $link POSTPONE: inline } " (as documented in " { $link "inference-combinators" } ") as well as " { $link POSTPONE: recursive } "."
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$nl
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"Furthermore, the input parameters which are quotations must be annotated in the stack effect. For example, the following will not infer:"
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{ $example ": bad ( quot -- ) [ call ] keep foo ; inline recursive" "[ [ ] bad ] infer." "Literal value expected\n\nType :help for debugging help." }
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{ $example ": bad ( quot -- ) [ call ] keep foo ; inline recursive" "[ [ ] bad ] infer." "Got a computed value where a literal quotation was expected\n\nType :help for debugging help." }
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"The following is correct:"
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{ $example ": good ( quot: ( -- ) -- ) [ call ] keep good ; inline recursive" "[ [ ] good ] infer." "( -- )" }
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"An inline recursive word cannot pass a quotation on the data stack through the recursive call. For example, the following will not infer:"
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{ $example ": bad ( ? quot: ( ? -- ) -- ) 2dup [ not ] dip bad call ; inline recursive" "[ [ drop ] bad ] infer." "Literal value expected\n\nType :help for debugging help." }
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{ $example ": bad ( ? quot: ( ? -- ) -- ) 2dup [ not ] dip bad call ; inline recursive" "[ [ drop ] bad ] infer." "Got a computed value where a literal quotation was expected\n\nType :help for debugging help." }
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"However a small change can be made:"
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{ $example ": good ( ? quot: ( ? -- ) -- ) [ good ] 2keep [ not ] dip call ; inline recursive" "[ [ drop ] good ] infer." "( object -- )" }
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"An inline recursive word must have a fixed stack effect in its base case. The following will not infer:"
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Slava Pestov