Create comma-separated lists in GNU Make

Question

I have a Makefile with a set of booleans which must be used to control the flags for an external application. The problem is that the flag must be passed as a comma-separated s

Answer 1

A construct like

OPTIONS+=$(if $(filter y,$(BOOL_A)),--with=A,--with-out=A)

should work.

Edit: Sorry, overlooked the necessary collation.

PARTS=A B C
YESSES=$(foreach i,$(PARTS),$(if $(filter y,$(BOOL_$(i))),$(i)))

all:
        echo with=$(shell echo $(YESSES) | tr ' ' ',')

The idea is to check for each possible part X whether it's set to yes and insert it into a list if it is yes. This list is whitespace-separated and hard to comma-separate with make, but easy to do this in shell.