:: Eq a => [a] -> [a] -> [a] -> [a] package:extra

Replace a subsequence everywhere it occurs.
replace "el" "_" "Hello Bella" == "H_lo B_la"
replace "el" "e" "Hello"       == "Helo"
replace "" "x" "Hello"         == "xHxexlxlxox"
replace "" "x" ""              == "x"
\xs ys -> replace xs xs ys == ys