Error with functions

Hey,
create or replace function sample(varchar,int) returns varchar as'
declare
        data alias for $1;
        size alias for $2;
begin
        return  substr(data,(length(data)-size)+1,length(data));
end;
' language 'plpgsql';
____________________________
WARNING:  plpgsql: ERROR during compile of sample near line 2
ERROR:  parse error at or near ";"

Can any body tell me why is this error coming
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Warm Regards
Shÿam Peri

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