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

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

4. Build the Makefile with cake3

   $ cake3

5. 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 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 if you are surprised. Cake3 implements .INTERMEDIATE pattern 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.

• Cake3 may generate different versions of Makefile at once

  We often want to generate developer's and end-user's makefiles. End-user version may want treat several rules as pre-executed. Cake3 easily allows us to do that by using 'slicing' utility. See ./Examples/GCC_SED/Cakefile.hs for details.

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.