To call or not to call

[Ken Smith]

I have experienced some strange behavior with call and eval which I'd
like to share.  I think I know how to work around the problem I'm
experiencing but I'd like to know why I'm seeing this behavior.  First,
the makefiles.

% cat test1.mk
define __func
        return_value:=0
endef

func=$(eval $(__func))$(return_value)

my_retval:=$(func)

all:
        @echo my_retval=$(my_retval)
        @echo return_value=$(return_value)

% cat test2.mk
define __func
        return_value:=0
endef

func=$(eval $(__func))$(return_value)

my_retval:=$(call func)

all:
        @echo my_retval=$(my_retval)
        @echo return_value=$(return_value)

% diff test1.mk test2.mk
7c7
< my_retval:=$(func)
---
> my_retval:=$(call func)

I read in the GNU make manual that "it doesn't make sense to use call
with no parameters" so I figured I'd be fine with $(func).  It turns out
that the output of `gmake -f test1.mk' looks quite strange.

% gmake -f test1.mk
my_retval=0ue:=0
return_value=0

Whereas the output of `gmake -f test2.mk' matches my expectations.

% gmake -f test2.mk
my_retval=0
return_value=0

Can someone tell me why?

  Ken