Agda Makefile
=============

A Makefile for building Agda projects, with dependencies downloaded by curl.

Example
-------

Imagine creating a project foo, with dependencies bar and baz. The makefile
for foo begins by declaring its dependencies:

  pkgid = foo
  dependencies = bar baz

and the dependency tarball URIs:

  export bar ?= http://example.com/bar.tgz
  export baz ?= http://example.com/baz.tgz

then it downloads and imports the common makefile:

  export agdamakefileuri ?= https://github.com/agda/agda-makefile/raw/v0.0.1/Makefile
  export agdamakefile ?= $(CURDIR)/build/share/make/agda-makefile
  export CURL ?= curl

  $(agdamakefile):
    $(CURL) --create-dir -o $@ $(agdamakefileuri)

  include $(agdamakefile)

At this point, foo's makefile has bootstrapped itself by downloading
and including the master Makefile. The rest of the makefile is as per
usual, but can make use of the target install-dependencies, which
downloads and installs the dependent projects. It can also use some
predefined targets for typechecking Agda files and generating htmt
documentation from Agda files:

  install-agda: $(agdadir)/Foo.agdai

  install-html: $(htmldir)/Foo.html

  install-doc:
    $(INSTALL) -D README $(docdir)
    $(INSTALL) -D LICENSE $(docdir)

  install: install-dependencies install-agda install-html install-doc

Assumptions
-----------

This all assumes quite a bit about the dependent projects:

1. They must have URIs which return a project tarball.

2. Each project contains top-level Makefiles: make will (rather inefficiently)
   search the project looking for Makefiles, searching recursively through
   the children of any directory which doesn't contain a Makefile.  Life
   will be better for all concerned if projects put a Makefile very close
   to top-level!

3. Each makefile should define at least the targets "clean" and
   "install", which should install files in the following directories:

     $(agdadir): Agda source files and interface files
     $(docdir): Documentation
     $(htmldir): HTML files

The environment variables their default values are:

  srcdir   = $(CURDIR)/src
  builddir = $(CURDIR)/build
  prefix   = $(builddir)
  datadir  = $(prefix)/share
  agdadir  = $(datadir)/agda
  tmpdir   = $(builddir)/tmp/$(pkgid)
  docdir   = $(datadir)/doc/$(pkgid)
  htmldir  = $(docdir)/html

There are targets:

  $(agdadir)/<filename>.agda:
    copies the file from $(srcdir)/<filename>.agda

  $(agdadir)/<filename>.agdai:
    typechecks $(agdadir)/<filename>.agda

  $(htmldir)/<filename>.html:
    generates documentation from $(agdadir)/<filename>.agda

To handle dependencies, there are targets:

  install-dependencies
  clean-dependencies

which download and unpack the dependencies, then recursively call make
install or make clean on them. 

There is very minimal version control: if make discovers that a
dependency has been defined as coming from two different URIs, then it
raises an error. The parent project can try to resolve this by
providing its own URI for the conflicting dependency.