SQL function problem in 7.1?

Am I doing something stupid with strings in SQL functions.


richardh=> select version();
                                version
------------------------------------------------------------------------
 PostgreSQL 7.1beta3 on i586-pc-linux-gnu, compiled by GCC egcs-2.91.66
(1 row)

richardh=> select * from foo;
 a |  b
---+-----
 1 | aaa
 2 | bbb
 3 | ccc
(3 rows)

richardh=> create function fooa(int) returns text as 'select b from foo
where a = $1;' language 'sql';
CREATE
richardh=> select fooa(2);
 fooa
------
 bbb
(1 row)

richardh=> create function foob(text) returns int as 'select a from foo
where b = ''$1'';' language 'sql';
CREATE
richardh=> select foob('bbb');
 foob
------

(1 row)


TIA

- Richard Huxton