Substitution references

[Phil Endecott]

Hi Make experts,

When I did this:

X=$(words Y)

test:
        echo $(X)
        echo $(X:Y=a b c)

I expected to get "1" and "3", but actually I got "1" and "1".
Is this the expected behaviour?  (GNU Make version 3.73).

What I was really trying to do was to use substitution references to
give a common interface to multiple programs that have the same
purpose but with different command-line formats.  My first idea
was (vaguely) like this:

if some-condition
DO_FOO=fooprog IN > OUT
else
DO_FOO=otherfoo -in IN -out OUT
endif

y: x
        $(DO_FOO:IN=x:OUT=y)

But of couse I can't do two substitututions in one go like this.  I could
go for this:
        $(subst IN,x,$(subst OUT,y,$(DO_FOO)))
but that's a bit long, so I tried this:

DO_FOO=fooprog $(word 1,IN_OUT) > $(word 2,IN_OUT)
or DO_FOO=otherfoo -in $(word 1,IN_OUT) -out $(word 2,IN_OUT)
and then
        $(DOO_FOO:IN_OUT=x y)
but this fails because the $(word...) functions seem to be applied before
IN_OUT is substituted.  It ends up doing "fooprog x y >" or
"otherfoo -in x y -out".

So, experts!, how would you do this?  Do you have a better solution
than the nested $(subst....) calls?  (In my real problem I have more than
just the two parameters).  My aim is to keep the rules where the pattern
is used simple, but I don't care how complex the definitions are.

Thanks in advance for your help.

--Phil.