Thoughts on make extensions

foo.mk

CC ?= gcc
CXX ?= g++

.PHONY: all

all: foo.o foopp.o

foo.o: foo.c
	$(CC) -c -o $< $@

foopp.o: foopp.cpp
	$(CXX) -c -o $< $@

hello.c

#include <stdio.h>
#include <hello.h>

int main() {
	printf("%s\n", hello);
	return 0;
}

hello.h.in

static const char * const hello = "@HELLO@";

namespaces.mk

CC ?= gcc
FOO_CC := gcc-1.0
CXX ?= g++

.PHONY: all

all: foo_all bar.o barpp.o

bar.o: bar.c
	$(CC) -c -o $< $@

barpp.o: barpp.cpp
	$(CXX) -c -o $< $@

# The second argument prefixes all variables with FOO_. If the generated
# variable is unset, it is set to the value of the bare variable.
# The third argument prefixes all rules with foo_.
include foo.mk FOO_ foo_

# This should result in the following execution:
# all {
#   foo_all {
#       foo.o {
#           foo.c (found)
#       } foo.o -> gcc-1.0 -c -o foo.o foo.c
#       foopp.o {
#           foopp.cpp (found)
#       } foopp.o -> g++ -c -o foopp.o foopp.cpp
#   } foo_all
#   bar.o {
#       bar.c (found)
#   } barpp.o -> gcc -c -o bar.o bar.c
#   barpp.o {
#       barpp.cpp (found)
#   } barpp.o -> g++ -c -o barpp.o barpp.cpp
# } all

nethack.mk

.EVAL_RULES := %.l!pre %.o!pre
.PHONY: all %.l!pre %.o!pre

all: nethack sokoban.l

nethack: nethack.o

levcc: levcc.c
	$(CC) -o $< $@

declgen: declgen.c
	$(CC) -o $< $@

decltab.h: decltab.s declgen
	declgen -o $< $@

%.l!pre: %.ld
	include $@

%.l: %.lev levcc
	levcc -o $< $@

%.o!pre: %.d
	include $@

%.o: %.c
	$(CC) -c $< $@

%.ld: %.lev levcc
	levcc -M -o $< $@

%.d: %.c
	${CC} -M -o $< $@

# Exeution should go as follows:
# make
# all {
#   nethack {
#       nethack.o!pre {
#           nethack.d {
#               nethack.c (found)
#           } nethack.d -> gcc -M -o nethack.d nethack.c # nethack.d = "nethack.o: declgen.d"
#       } nethack.o!pre -> include nethack.d
#       nethack.o {
#           nethack.c (found)
#           decltab.h {
#               decltab.s (found)
#               declgen {
#                   declgen.o!pre {
#                       declgen.d {
#                           declgen.c (found)
#                       } declgen.d -> gcc -M -o declgen.d declgen.c
#                   } declgen.o!pre -> include declgen.d
#                   declgen.o {
#                       declgen.c (found)
#                   } declgen.o -> gcc -c -o declgen.o declgen.c
#               } declgen -> gcc -o declgen declgen.o
#           } decltab.h -> declgen -o decltab.h decltab.s
#       } nethack.o -> gcc -c nethack.o nethack.c
#   } nethack -> gcc -o nethack nethack.o
#   sokoban.l!pre {
#       sokoban.ld {
#           sokoban.lev (found)
#           levcc {
#               levcc.o!pre {
#                   levcc.d {
#                       levcc.c (found)
#                   } gcc -M -o levcc.d levcc.c
#               } levcc.o!pre -> include levcc.d
#               levcc.o {
#                   levcc.c (found)
#               } levcc.o -> gcc -c -o levcc.o levcc.c
#           } levcc -> gcc -o levcc levcc.o
#       } sokoban.ld -> levcc -M -o sokoban.ld sokoban.lev # sokoban.ld = "sokoban.l: monsters.m"
#   } sokoban.l!pre -> include sokoban.ld
#   sokoban.l {
#       monsters.m (found)
#   } sokoban.l -> levcc -o sokoban.l sokoban.lev
# } all

simple.mk

.EVAL_RULES := %.o!pre
.PHONY: all %.o!pre

all: hello

hello: hello.o
	$(CC) -o $< $@

%.h: %.h.in
	sed -e 's/@HELLO@/Hello World!/g' $@ > $<

%.d: %.c
	$(CC) -M -o $< $@

%.o!pre: %.d
	include $@

%.o: %.c
	$(CC) -c -o $< $@

# Execution should go as follows:
# all {
#   hello {
#       hello.o!pre {
#           hello.d {
#               hello.c (found)
#           } hello.d -> gcc -M -o hello.d hello.c
#       } hello.o!pre -> include hello.d
#       hello.o {
#           hello.c (found)
#           hello.h { # added by hello.d
#               hello.h.in (found)
#           } hello.h -> sed -e 's/@HELLO@/Hello World!/g' hello.h.in > hello.h
#       } hello.o -> gcc -c -o hello.o hello.c
#   } hello -> gcc -o hello hello.o
# } all