combinators.smart: "keep-inputs" combinator

basis/combinators/smart/smart-docs.factor

@@ -106,11 +106,21 @@ HELP: append-outputs-as
 
 { append-outputs append-outputs-as } related-words
 
+HELP: drop-outputs
+{ $values { "quot" quotation } }
+{ $description "Calls a quotation and drops any values it leaves on the stack." } ;
+
+HELP: keep-inputs
+{ $values { "quot" quotation } }
+{ $description "Calls a quotation and preserves any values it takes off the stack." } ;
+
+{ drop-outputs keep-inputs } related-words
 
 ARTICLE: "combinators.smart" "Smart combinators"
 "A " { $emphasis "smart combinator" } " is a macro which reflects on the stack effect of an input quotation. The " { $vocab-link "combinators.smart" } " vocabulary implements a few simple smart combinators which look at the static stack effects of input quotations and generate code which produces or consumes the relevant number of stack values." $nl
-"Call a quotation and discard all output values:"
+"Call a quotation and discard all output values or preserve all input values:"
 { $subsection drop-outputs }
+{ $subsection keep-inputs }
 "Take all input values from a sequence:"
 { $subsection input<sequence }
 "Store all output values to a sequence:"

basis/combinators/smart/smart.factor

@@ -7,6 +7,9 @@ IN: combinators.smart
 MACRO: drop-outputs ( quot -- quot' )
     dup infer out>> '[ @ _ ndrop ] ;
 
+MACRO: keep-inputs ( quot -- quot' )
+    dup infer in>> '[ _ _ nkeep ] ;
+
 MACRO: output>sequence ( quot exemplar -- newquot )
     [ dup infer out>> ] dip
     '[ @ _ _ nsequence ] ;