commafy : string list -> string list
STRUCTURE
SYNOPSIS
Add commas into a list of strings.
DESCRIPTION
An application commafy [s1,...,sn] yields [s1, ",", ..., ",", sn].
FAILURE
Never fails.
EXAMPLE
- commafy ["donkey", "mule", "horse", "camel", "llama"];
> val it =
    ["donkey", ", ", "mule", ", ", "horse", ", ", "camel", ", ", "llama"] :
  string list

- print (String.concat it ^ "\n");
donkey, mule, horse, camel, llama
> val it = () : unit

- commafy ["foo"];
> val it = ["foo"] : string list

HOL  Kananaskis-10