## NB ##

These notes reflect earlier thinking about the language and may not
necessarily accurately describe the current goaljobs language.  Please
read the documentation instead.

## NB ##

Like 'make' except:
 - Predicates can be based on arbitrary expressions, not just
   "file X is older than file Y".
 - Rules are more flexible and encourage structuring and reuse
   through functions.
 - Goals can be parameterized.
 - Program can run continuously to implement business rules.

Differences from 'whenjobs':
 - Goals instead of variables.
 - Persistent (across session) variables exist, but are not central.
 - Doesn't use <<..>> for shell scripts (has a function 'sh' instead).
 - No daemon.

Similarities to 'whenjobs':
 - Each shell script runs in its own temporary directory.

Example program:

  let package = "foo"

  let rec goal website_updated version =
    let tarfile = sprintf "%s-%s.tar.gz" package version in
    let tarpath = getenv "HOME" // "html" // tarfile in
    let url = sprintf "http://example.com/%s" tarfile in

    target (url_exists url);

    require (tarball_exists version);
    require (tarball_tested version);

    sh "rsync %s example.com:/html/" tarpath

  and goal tarball_tested version =
    let tarfile = sprintf "%s-%s.tar.gz" package version in
    let tarpath = getenv "HOME" // "html" // tarfile in
    let memkey = package ^ "_tested_" ^ version in

    target (memory_exists memkey);

    require (tarball_exists version);

    sh "
      tar zxf %s
      cd %s-%s
      ./configure
      make
      make check
    " tarpath package version;

    memory_set memkey "1"

  and goal tarball_exists version =
    let tarpath = getenv "HOME" // "html" // tarfile in
    target (file_exists tarpath);
    sh "
      cd $HOME/repos/%s
      git fetch
      git archive --prefix %s-%s/ v%s | gzip > %s-t
      mv %s-t %s
    " package package version version tarpath tarpath tarpath

  every 1 hour =
    let version = shout "
      cd $HOME/repos/%s
      git fetch
      git describe --tags --abbrev=0 --match='v*'
    " package in
    require (website_updated version)

This compiles down to a command line program that can be used like this:

  ./compile [-flags] [goals]

The goals are not enabled automatically.  You have to do something
(simple) to publish a goal and specify how command line arguments get
mapped to goal arguments, since the mapping is not likely to be 1-1
strings.  In the end you can do stuff like:

  ./compile all
  ./compile clean
  ./compile build program  # program is a parameter
  ./compile -my-flag       # custom flags can be defined