Propositions as Filenames, Builds as Proofs: The Essence of Make

Propositions as Filenames, Builds as Proofs: The Essence of Make(bentnib.org)

77 points by archena 11 years ago | 19 comments

alanpost 11 years ago |

> The essence of make is this: make is an implementation of constructive logic programming

To be perfectly pedantic, the essence of make is that it is an expert system for traversing a directed acyclic graph (DAG).

It works by constructing a graph of “filenames” (vertices) and the commands required to create those files (directed edges). Using that as it’s knowledge base, make performs a reverse topological sort on the target filename to determine the graph traversal necessary to create it’s target file, and runs each command in the traversal so as to arrive at that target. Since it has a list of all intermediate vertices that must exist before it’s target can exist, make is further able to determine whether it needs to run a command or whether it can use the cached result.

I don’t think the author is doing us any favors by trying to fit make’s behavior in to a constructive logic system. It’s missing operators for doing that, as the author states: “Note that the form of compound propositions allowed is extremely restricted, even by the standards of logic programming.”

I find the author’s conclusions then a mixed bag. They would be good conclusions if make was a constructive logic system, but it’s not, it’s an expert system for traversing a DAG. I think of make as a “workstate” system: do what you need to do to put my build in a particular state, whereas most of the author’s conclusions center around “workflow:” move this unit of work through it’s lifecycle.[1] Make only performs that work incidentally to putting your build in a particular state.

1: The workflow/workstate distinction is not my idea. It’s explored in “Adaptive Software Development” by James A. Highsmith III.

[I originally made this comment at https://lobste.rs/s/rqf3f5/propositions_as_filenames_builds_...]

asQuirreL 11 years ago | |

To build on the pedantry, make would be traversing a restricted form of directed acyclic hyper-graph, no? The edges are between sets of vertices to a single vertex.

I found these structures cropping up alongside Horn clauses, and Context-Free Grammars in interesting ways. In this case, viewing make rules as Horn clauses allows us to use a variant of Horn-SAT to find the minimum set of files we have to produce to build a rule, which is interesting to think about, and reason about.

This article felt as though it was food for thought and not really trying to push any particular idea too hard. In any case, I found it interesting as it found parallels to the sorts of structures I found when exploring various algorithms for Context-Free Grammars (such as pruning, or detecting erasable non-terminals, which can both be described in terms of Horn-SAT).

mbreese 11 years ago | | |

Well, you have a large graph defined with multiple end points, so the DAG itself doesn't necessarily point to any single vertex. Only once you define which endpoint you want does it collapse.

adekok 11 years ago |

There is a bottom-up build system: http://gittup.org/tup/

It's very nice, but the cost of changing from Make means that most people don't use it. The Ninja design docs reference Tup, so they're aware it exists.

Solving the Latex problem of “Label(s) may have changed. Rerun to get cross-references right.” is hard. The assumption of make is that the only state is in the file system. i.e. running the same inputs should produce the same outputs. The above message shows that Latex violates this constraint.

The simple solution is to (ugh) write a wrapper script which runs Latex, and creates another output file if the labels are wrong. Only after the labels are right does the output file stop changing.

Which means the dependencies are a circular loop. Which Make doesn't handle. <sigh>

The limitations of 1970s design is apparent. But Make is so astonishingly powerful that anything new has to be much better than Make. So far that doesn't seem to have happened.

rwmj 11 years ago |

If anyone's interested, I generalized make to work beyond files (eg: if the tarball doesn't exist on the website already, then it must be uploaded; before uploading, the tarball must have been tested). Also to add parameters to rules, which work a bit like .c.o: rules in make, but fully general with multiple parameters.

To be fair I haven't worked hard to make this very usable, but I do use it myself a lot for all sorts of interesting things:

The tool itself: http://git.annexia.org/?p=goaljobs.git;a=summary

A subset of recipes I use regularly: http://git.annexia.org/?p=goals.git;a=summary

bandrami 11 years ago |

Personally I've found make incredibly useful as an init system (though it takes a static make in /bin). I have targets like mount_a, %.start, %.stop (those both turned out to be overkill so I just wrote the start/stop targets by hand, but it works fine), halt, etc.

Works great, is very lightweight, does away with the antiquated idea of integral runlevels, and is very easy to debug. Plus you can probably set it up in a single afternoon and then just boot with init="/bin/make -f /etc/init.mk multi_user".

lindig 11 years ago |

I believe that one crucial feature of Make is that it does not plan the construction of a target from start to finish but that construction and planning are interleaved: Make does not look at the file system and build a plan which it then executes but it only executes the next step and then looks at the file system again. This precludes using Make to create a shell script (much like a compiler) which is then executed. I'm not sure that this interleaving is present in the description of Make in the article being discussed.

Edits: typos.