PostgreSQL syntax to add the day to a date column

pg_add_day_date.sql

case extract(isodow from ~~date~~)
    when 1 then 'Mon ' || cast(~~date~~ as date)
    when 2 then 'Tue ' || cast(~~date~~ as date)
    when 3 then 'Wed ' || cast(~~date~~ as date)
    when 4 then 'Thu ' || cast(~~date~~ as date)
    when 5 then 'Fri ' || cast(~~date~~ as date)
    when 6 then 'Sat ' || cast(~~date~~ as date)
    when 7 then 'Sun ' || cast(~~date~~ as date)
end date