ERROR: $1 is declared CONSTANT in plpgsql - Mailing list pgsql-novice

Hello folks,
I wrote my first plpgsql-functions for PostgreSQL 7.1.3. I try to
convert Ascii-Strings in HTML-conform Strings  (Converting 'Äquator' ->
'Äquator') ... Now I get a error message like this:

NOTICE:  plpgsql: ERROR during compile of f_ascii2html near line 7
ERROR:  $1 is declared CONSTANT

For me $1, or better InpAscii is not CONSTANT ... I cannot find the
mistake ... Can anybody help out?

Hopefully, you can reproduce the error with the code right here.

Thanks a lot,
Hans

PS:
There is some debug-code that I have not used because the functions does
not work ;-)).

-- BEGIN OF SKRIPT ...


DROP TABLE t_ascii2html;

/* table for replacing letters */

CREATE TABLE t_ascii2html (
    ascii VARCHAR(1),
    html VARCHAR(20)
);

INSERT INTO t_ascii2html VALUES ('ä','ä');
INSERT INTO t_ascii2html VALUES ('ö','ö');
INSERT INTO t_ascii2html VALUES ('ü','ü');
INSERT INTO t_ascii2html VALUES ('Ä','ä');
INSERT INTO t_ascii2html VALUES ('Ö','ö');
INSERT INTO t_ascii2html VALUES ('Ü','ü');
INSERT INTO t_ascii2html VALUES ('ß','ß');
INSERT INTO t_ascii2html VALUES ('"','"');
INSERT INTO t_ascii2html VALUES ('&','&');
INSERT INTO t_ascii2html VALUES ('<','<');
INSERT INTO t_ascii2html VALUES ('>','>');


DROP FUNCTION f_ascii2html(TEXT);


/* Converting 'special' letters (eg. german umlaute like "ö") into a
HTML-conform string */

CREATE FUNCTION f_ascii2html(TEXT)
    RETURNS TEXT
    AS '
        DECLARE
        InpAscii ALIAS FOR $1;
        CharMap RECORD;
        InsertPosition INTEGER;
        Part1 TEXT;
        Part2 TEXT;
        BEGIN
        InpAscii := $1;

            -- Select all datasets from the table describing the replacement
            FOR CharMap IN SELECT * FROM f_ascii2html LOOP
                RAISE NOTICE ''CharMap --- ASCII: %, HTML: %'', t_ascii2html.ascii,
t_ascii2html.html;

                WHILE InpAscii ~ CharMap.ascii
                    RAISE NOTICE ''INPASCII: %'', InpAscii;
                    SELECT position(InpAscii IN CharMap.ascii)
                    INTO InsertPosition;
                    RAISE NOTICE ''INSERTPOSITION: %'', InsertPosition;
                    SELECT substrg(InpAscii FROM (InsertPosition - 1))
                    INTO Part1;
                    RAISE NOTICE ''PART1: %'', Part1;
                    SELECT substrg(InpAscii FROM (InsertPosition + 1))
                    INTO Part2;
                    RAISE NOTICE ''PART2: %'', Part2;
                    InpAscii := Part1 || CharMap.html || Part2 ;
                    RAISE NOTICE ''INPASCII: %'', InpAscii;
                END LOOP;
            END LOOP;
        RAISE NOTICE ''InpAscii: %'', InpAscii;
        RETURN InpAscii
        END;
       '

     LANGUAGE 'plpgsql';

/* Sample: Converting 'Äquator' -> 'Äquator' */

select f_ascii2html('Äquator');

/* I get the following error message:
NOTICE:  plpgsql: ERROR during compile of f_ascii2html near line 7
ERROR:  $1 is declared CONSTANT
*/