cake3-0.5.0.0: README.md
Cake3
=====
Cake3 is a EDSL for building Makefiles, written in Haskell. With cake3,
developer can write their build logic in Haskell, obtain clean and safe Makefile
and distribute it among the non-Haskell-aware users. Currenly, GNU Make is
the only backend supported.
The Goals
---------
Make is a build tool which was created more than 20 yesrs ago. It has a number
of versions and dialects. Basic Makefiles are really easy to write and
understand. Unfortunately, it is hard to write real-world scale set of rules
correctly due to tricky syntax and lots of pitfails. As of today, Make has
automatic, declarative and imperative variables, builtin rules, pattern-rules,
double-colon rules, C-style ifdefs (which doesn't work well with declarative
variables) and lots of other strange things. Nevertheless, it is still widely
used as a de-facto standard tool which everyone has access to.
The goals of Cake3 are to help the developer to:
* Stop overusing Make by writing complex logic in make-language
* Still have a correct Makefile which could be distributed among the end-users
* Practice some Haskell
Installation
------------
From Hackage:
$ cabal install cake3
From the Github:
1. Install [Haskell Platform](http://www.haskell.org/platform/)
2. Install dependencies
$ cabal install haskell-src-meta monadloc QuasiText
3. Build the thirdcake from Github
$ git clone http://github.com/grwlf/cake3
$ cd cake3
$ cabal configure && cabal install
Usage
-----
1. Create the Cakefile.hs in the root dir of your project
$ cake3 init
2. Edit Cakefile.hs, fill it with rules or other logic you need
$ vim Cakefile.hs
3. Debug your generator with
$ cake3 ghci
Prelude> :lo Cakefile.hs
3. Build the Makefile with cake3
$ cake3
4. Run GNU make as usual
How does it work
----------------
Cake3 allows user to write Cakefile.hs in plain Haskell to define rules, targets
and other things as usual. `cake3` executable compiles it into ./Cakegen
application which outputs your Makefile (ghc is required for that). GNU Make
knows how to do the rest.
### Example
Here is the example of simple Cakefile.hs:
module Cakefile where
import Development.Cake3
import Cakefile_P
main = writeMake (file "Makefile") $ do
selfUpdate
cs <- return $ [file "main.c", file "second.c"]
d <- rule $ do
shell [cmd|gcc -M $cs -MF @(file "depend.mk")|]
os <- forM cs $ \c -> do
rule $ do
shell [cmd| gcc -c $(extvar "CFLAGS") -o @(c.="o") $c |]
elf <- rule $ do
shell [cmd| gcc -o @(file "main.elf") $os |]
rule $ do
phony "all"
depend elf
includeMakefile d
* Cakefile\_P is an autogenerated module. It defines `file :: String -> File`
function plus some others.
* Main building blocks - `rule` functions - build Makefile rules one-to-one.
The prerequisites are computed based on it's actions.
* All actions live in Action monad (`A` Monad). `shell` is the most important
operation of this monad.
* Quasy-quotation is used to simplify writing of the shell code. `[cmd|..|]`
takes a string as an argument. The following antiquotations are supported:
* $name antiquotes Hasell expressions `name` of type File, Variable, few
others. The name will be placed to the set of prerequisites of the rule.
* @name antiquotes Hasell expressions `name` of type File. The name will be
placed to the set of rule's targets.
* complex Haskell expressions inside antiquotations are supported with
$(foo bar) and @(bar baz) syntax.
* $$ and @@ expands to $ and @.
* Rules appears in the Makefile in the reversed order. Normally, you want
'all' rule to be defined at the bottom of Cakefile.hs.
* Starting from 0.4, cake3 outputs rule named 'clean' automatically. This rule
contains recipe which deletes all intermediate files with 'rm' command.
* `selfUpdate` call includes the self-updating dependencies. That means, that
Makefile will depend on Cakefile.hs and thus will require ghc to present in
the system. Removing `selfUpdate` call will make the Makefile fully
Haskell-independent.
Features and limitations
------------------------
Thirdcake follows Autoconf's path in a sence that it builds the program may do
some checks and tests and generates the Makefile. In the same time, the idea of
this EDSL is to move as much logic as possible in the final Makefile, to drop
the cake3 dependency at the build time.
Of cause, it is possible up to some degree. For example, Cake3 doe not provide a
way to scan the project tree with Make's wildcards. But it is possible and may
be implemented in future.
Still, some common patterns are supported so I hope that users would call
resulting Makefiles safe and robust enough for, say, package maintainers.
### Features
* *Cake3 generates the 'clean' rule automatically.*
But if you define your own 'clean', cake3 will take it as is.
* *Cake3 takes care of spaces inside the filenames.*
Everyone knows that Makefiles don't like spaces in filenames. Cake3
carefully inserts '\ ' to make make happy.
* *Cake3 rebuilds a rule's target when variable changes.*
Consider following antipattern:
# You often write rules like this, don't you?
program : program.c
gcc $(FLAGS) -o $@ $^
Unfortunately, changes in FLAGS don't lead to rebuilding of the program.
Hardly-trackable bugs may appear if one part of a project was built with one
set of optimisation flags and another part was build with another set by
mistake.
Thirdcake implements the makevar checksum
[pattern](http://stackoverflow.com/a/17830736/1133157) from StackOverflow to
detect changes in variables and rebuild targets when nessesary.
rule $ do
shell [cmd|gcc $(extvar "FLAGS") -o @program $program_c |]
will rebuild `program` every time the FLAGS change
* *Rules may have more than one target.*
It is not that simple to write a rule which has more than one target in
Makefile. Indeed,
out1 out2 : in1 in2
foo in1 in2 -o out1 -o out2
is not corret. Read this [Automake
article](http://www.gnu.org/software/automake/manual/html_node/Multiple-Outputs.html#Multiple-Outputs)
if you are surprised. Cake3 implements [.INTERMEDIATE
pattern](http://stackoverflow.com/a/10609434/1133157) to deal with this
problem so `rule` like this
rule $ do
shell [cmd|foo $in1 $in2 -o @out1 -o @out2 |]
will always notice inputs changes and rebuild both outputs
* *Cake3 supports global prebuild\postbuild actions*
Common human-made Makefile with prebuild commands would support them for one
rule, typically, "all". Other targets often stay uncovered. Cake3 makes sure
that actions are executed for any target you call.
* *Cake3 lets user organize build hierarchy.*
Say, we have a project A with subproject L. L has it's own Makefile and we
want to re-use it from our global A/Makefile. Make provides only two ways of
doing that. We could either include L/Makefile or call $(MAKE) -C L. First
solution is a pain because merging two Makefiles together is generally a
hard work. Second approach is OK, but only if we don't need to pass
additional paramters or depend on a specific rule from L.
Thirdcake's approach in this case is a compromise: since it employs
Haskell's module system, it is possible to write:
-- Project/lib/CakeLib.hs
import CakeLib_P.hs
librule = do
rule $ do
shell [cmd|build a lib|]
-- Project/Cakefile.hs
import Cakefile_P.hs
import CakeLib.hs
-- ^ note the absence of lib folder here. cake3 will copy all Cake*hs to
-- the temp dir, then build them there.
all = do
lib <- librule
rule $ do
shell [cmd|build an app with $lib |]
A/Cakefile.hs and do whatever you want to. Resulting makefiles will always
be monolitic.
### Limitations
#### Make syntax
As a summary - only a samll subset of Make syntax is supported. For complex
algorithms Haskell looks more suitable so implement everything you need inside
the Cakefile.hs. In particular:
* Cake3 offers no way of detecting directory content chages at the moment. For
example, user has to rerun the ./Cakegen if they add/remove a source file.
* Cake3 doesn't check the contents of Makefile variables. It is user's
responsibility to keep them safe.
* DSL doesn't allow to place Make variables anywhere except the recipe.
#### General
* Resulting Makefile is actually a GNUMakefile. GNU extensions (shell function
and others) are needed to make various tricks to work. Also, posix
environment with coreututils package is required. So, Linux, Probably Mac,
Probably Windows+Cygwin are the platforms which run cake3.
* All Cakefiles across the project tree should have unique names in order to
be copied. Duplicates are found, the first one is used
Random implementation details
-----------------------------
1. cake3 script copies all the Cake\*hs files it found in the project tree to
a single temporary directory before compiling the ./Cakegen application.
That is why all the cakefiles in project should have different names.
Another consequence - cakefiles as Haskell modules may be imported by
filename regardles of their actual position in the project tree.
2. Cake3 creates ./Cake\*\_P.hs files for every Cake\*hs. The \_P files
contain paths information. In particular, they define `file` function for
the current directiory. `selfUpdate` function is also defined there.
3. All filepaths in the final Makefile are relative.
4. Cake3 uses it's own representation of files (File). Many filepath functions
(takeDirectory, takeBaseName, dropExtensions, </>, etc) are defined for
File as members of FileLike typeclass. See System.FilePath.Wrapper for the
details.