tablename as function parameter

I'm trying to create a function (language 'sql') with table name as single input parameter,
but I always get syntax errors at "$1". Probably I am use wrong types.

simple example:

create function testfct (text) language sql as 'select count(*) from $1'

fails.

I tested type alternatives to 'text' , such as 'name' or 'sql_identifier' - no success.

What is the right type ?