functions and columns are equivalent

gistfile1.txt

svilain=# create table f (foo int);
CREATE TABLE
svilain=# create or replace function bar(f) returns int language sql as $$ select $1.foo + 10 $$;
CREATE FUNCTION
svilain=# insert into f values (1), (2);
INSERT 0 2
svilain=# select f.foo, f.bar from f;
 foo | bar 
-----+-----
   1 |  11
   2 |  12
(2 rows)

svilain=#