Recursive LAMBDA to replace characters by specific substitutes from a lookup table

Question

The goal is to iterate through rows of the character table and replace each character with it's substitute.

The character table in this example is ={"&","&amp;";"<","&lt;";">","&gt;";"'","&apos;";"""","&quot;"}, or:

*(Sidenote: "&","&" must be last on the list in this exact case, or it will replace other occurrences from previous substitutions, since we're going last to first.)

Formula:

=LAMBDA(XML,Pos,
LET(
Cls,{"&","&amp;";"<","&lt;";">","&gt;";"'","&apos;";"""","&quot;"},
Row,IF(ISOMITTED(Pos),ROWS(Cls),Pos),
Crf,INDEX(Cls,Row,1),
Crr,INDEX(Cls,Row,2),
Sub,SUBSTITUTE(XML,Crf,Crr),
IF(Row=0,XML,ENCODEXML(Sub,Row-1))
))

Expected result for =ENCODEXML("sl < dk & jf") would be sl < dk &amp jf
I'm getting #VALUE! error instead.

Answer 1

1. You need to have an exit on the recursive:

=LAMBDA(XML,Pos,
LET(
Cls,{"&","&amp;";"<","&lt;";">","&gt;";"'","&apos;";"""","&quot;"},
Row,IF(ISOMITTED(Pos),ROWS(Cls),Pos),
Crf,INDEX(Cls,Row,1),
Crr,INDEX(Cls,Row,2),
Sub,SUBSTITUTE(XML,Crf,Crr),
IF(Row>1,ENCODEXML(Sub,Row-1),Sub)
))

2. You need to add the , in the call:

=ENCODEXML("sl < dk & jf",)

Or as @Filcuk discovered(and I learned just now) if it is optional it needs to be declared using []

ie:

=LAMBDA(XML,[Pos],
LET(
Cls,{"&","&amp;";"<","&lt;";">","&gt;";"'","&apos;";"""","&quot;"},
Row,IF(ISOMITTED(Pos),ROWS(Cls),Pos),
Crf,INDEX(Cls,Row,1),
Crr,INDEX(Cls,Row,2),
Sub,SUBSTITUTE(XML,Crf,Crr),
IF(Row>1,ENCODEXML(Sub,Row-1),Sub)
))

Then the , is not needed:

=ENCODEXML("sl < dk & jf")