Add nsequence

basis/generalizations/generalizations-docs.factor

@@ -2,6 +2,16 @@ USING: help.syntax help.markup kernel sequences quotations
 math arrays ;
 IN: generalizations
 
+HELP: nsequence
+{ $values { "n" integer } { "seq" "an exemplar" } }
+{ $description "A generalization of " { $link 2sequence } ", "
+{ $link 3sequence } ", and " { $link 4sequence } " "
+"that constructs a sequence from the top " { $snippet "n" } " elements of the stack."
+}
+{ $examples
+    { $example "CHAR: f CHAR: i CHAR: s CHAR: h 4 \"\" nsequence ." "\"fish\"" }
+} ;
+
 HELP: narray
 { $values { "n" integer } }
 { $description "A generalization of " { $link 1array } ", "
@@ -9,6 +19,8 @@ HELP: narray
 "that constructs an array from the top " { $snippet "n" } " elements of the stack."
 } ;
 
+{ nsequence narray } related-words
+
 HELP: firstn
 { $values { "n" integer } }
 { $description "A generalization of " { $link first } ", "
@@ -127,11 +139,15 @@ HELP: nkeep
 { $see-also keep nslip } ;
 
 ARTICLE: "generalizations" "Generalized shuffle words and combinators"
-"A number of stack shuffling words and combinators for use in "
+"The " { $vocab-link "generalizations" } " vocabulary defines a number of stack shuffling words and combinators for use in "
 "macros where the arity of the input quotations depends on an "
 "input parameter."
+$nl
+"Generalized sequence operations:"
 { $subsection narray }
+{ $subsection nsequence }
 { $subsection firstn }
+"Generated stack shuffle operations:"
 { $subsection ndup }
 { $subsection npick }
 { $subsection nrot }
@@ -139,6 +155,7 @@ ARTICLE: "generalizations" "Generalized shuffle words and combinators"
 { $subsection nnip }
 { $subsection ndrop }
 { $subsection nrev }
+"Generalized combinators:"
 { $subsection ndip }
 { $subsection nslip }
 { $subsection nkeep }

basis/generalizations/generalizations.factor

@@ -5,10 +5,13 @@ USING: kernel sequences sequences.private namespaces math
 math.ranges combinators macros quotations fry arrays ;
 IN: generalizations
 
-MACRO: narray ( n -- quot )
-    [ <reversed> ] [ '[ , f <array> ] ] bi
+MACRO: nsequence ( n seq -- quot )
+    [ drop <reversed> ] [ '[ , , new-sequence ] ] 2bi
     [ '[ @ [ , swap set-nth-unsafe ] keep ] ] reduce ;
 
+MACRO: narray ( n -- quot )
+    '[ , { } nsequence ] ;
+
 MACRO: firstn ( n -- )
     dup zero? [ drop [ drop ] ] [
         [ [ '[ , _ nth-unsafe ] ] map ]