ichar

I moved from postgres 7.0.2 to 8.0.1,

in the 7.0.2 version I process the next query, and it succeed:

select ichar(letra_ascii) || '-' || substr('00000' ||num_factura,length
(num_factura)+1,5) as factura from facturas 

but in 8.0.1 it outputs the next error:

ERROR:  not exist the function ichar(integer) 
HINT:  any function match with the arguments types.
Add explicit cast of types