-{ $values { "i" "a non-negative integer" } { "seq" "a mutable sequence" } { "quot" { $quotation "( i -- elt )" } } { "elt" object } }
-{ $description "If the sequence does not contain at least " { $snippet "i" } " elements or if the " { $snippet "i" } "th element of the sequence is " { $link f } ", calls the quotation to produce a new value, and stores it back into the sequence. Otherwise, this word outputs the " { $snippet "i" } "th element of the sequence." }
{ $description "Outputs the index of the first element in the sequence equal to " { $snippet "obj" } ". If no element is found, outputs " { $link f } "." } ;