Filter takes a predicate p and a list xs, and returns a list containing only those elements of xs that satisfy p. For example,

#math150#

Filter~(Lessthan~1)~[1, 2, 3]

#tex2html_wrap_indisplay2606# : #tex2html_wrap_indisplay2607#Foldr#tex2html_wrap_indisplay2608#@<8<#5#><896>><#891#>#tex2html_wrap_indisplay2609##tex2html_wrap_indisplay2610#! :}#tex2html_wrap_indisplay2611#1 ;SPMlt; < <349>>[1, 2, 3]

#math151#

Filter~p

Foldr~(Lift~p~Cons~Second )~Nil