mjhjmtu

I'm trying to build a macro
that processes a comma-separated-list of elements
so that:

MapAndUsea,b,c

would produce:

My first intuition is to use a expl3 combination
of seq_map* to process each element in turn
(here, wrap into parentheses)
then seq_use* to organize them around -- markers.

But this does not work as expected:

documentclassstandalone

usepackageexpl3
usepackagexparse

ExplSyntaxOn

NewDocumentCommandMapAndUse m %
 seq_set_from_clist:Nn l_raw_seq #1
 seq_map_variable:NNn l_raw_seq i (i)
 % seq_show:N l_raw_seq
 seq_use:Nn l_raw_seq -- 


ExplSyntaxOff

begindocument

MapAndUsea,b,c

enddocument

Since it produces:

From what I understand:

• from the doc: seq_map_* macros directly expand to the input stream.


• from seq_show:N l_raw_seq: the sequence is not actually affected by theseq_map command (elements are not parenthesized)

The sequence l_raw_seq contains the items (without outer braces):
> a
> b
> c.

How do I process each element "in place" with seq_map* without having them
pushed to the input stream?

Naive tries:

• 
  seq_set_from_clist:Nx l_processed_seq seq_map_variable:NNn l_raw_seq i ,(i): does not compile in consistence with the doc: this Nx variant
  does not exist, and seq_map* cannot be expanded this way into another
  "variable".


• 
  UseMapa,b,c with a 2-stages processing: does not work as expected
  since Mapa,b,c remains unexpanded.

Is there anything I've missed about expl3 logic there?

Is it possible to process my comma-separated input this way?

Are there alternatives or workarounds?

You can use two sequences; first apply the mapping to get the “adorned” items, then use them.

documentclassarticle

usepackageexpl3
usepackagexparse

ExplSyntaxOn

seq_new:N l__iagolito_in_seq
seq_new:N l__iagolito_out_seq

NewDocumentCommandMapAndUse m 
 
 seq_set_from_clist:Nn l__iagolito_in_seq #1 
 seq_set_map:NNn l__iagolito_out_seq l__iagolito_in_seq (exp_not:n ##1 ) 
 seq_use:Nn l__iagolito_out_seq ~--~


ExplSyntaxOff

begindocument

MapAndUsea,b,c

enddocument

An extended version where you can specify how to adorn the items and what to use between them:

documentclassarticle

usepackageexpl3
usepackagexparse

ExplSyntaxOn

seq_new:N l__iagolito_in_seq
seq_new:N l__iagolito_out_seq

NewDocumentCommandMapAndUse mmm 
 
 cs_set_protected:Nn __iagolito_mapanduse:n #2 
 seq_set_from_clist:Nn l__iagolito_in_seq #1 
 seq_set_map:NNn l__iagolito_out_seq l__iagolito_in_seq
 
 __iagolito_mapanduse:n exp_not:n ##1 
 
 seq_use:Nn l__iagolito_out_seq #3 


ExplSyntaxOff

begindocument

MapAndUsea,b,c(#1) -- 

enddocument