SQL UDF: Logical versus character

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If I have a subprocedure defined as:
     D VALIDTPNBR      PR              N
     D TPTTYPE                             LIKE(TPTYPE.TPTTYPE) CONST
     D TPNBR                               LIKE(TPNBR.TPNBR) CONST

And define a function as:
create function WEB/VALIDTPNBR (CHAR (8), CHAR (10))
returns CHAR (1)
simple call
language rpgle
deterministic
reads sql data
returns null on null input
no external action
allow parallel
external name 'WEB/WEBSRV(VALIDTPNBR)';

It seems that I get a MCH3601 everytime the following line executes:
return rValidTpNbr;

I am suspecting it is because N is not the same as 1A.
And as far as I know 'create function' doesn't support rpg indicator
variables.  Therefore I suspect I have to create a separate subprocedure
for my function which returns it as a character.

Later, I think I just heard Fred Flinstone scream Yabba Dabba Do and
boogie for the parking lot.

Rob Berendt
--
"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety."
Benjamin Franklin