[antlr-interest] String concatenation expression rule

[franck102]

I am writing a grammar for a fairly complex expression language, and in
particular I need to support string concatenation which is performed simply
by separating string literals with a space; and which automatically converts
other expressions to a string if needed to concatenate:
"a" "b" -> "ab"
2+3 "mm" -> "5mm"

I suspect I could use predicates to write a rule like this:

concatExpression
        :        ( expression | STRING_LITERAL )+ { apply only if at least
one of the elements is a string literal }?

Is there a way to achieve this? The alternative formulations I can think of
are pretty messy...
Thanks!

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