function_missing # lost in complexity

Capturing and assembling textual elements from rules This article builds on the previous ones, featuring a small parser for Org Mode files. I use the Clocking feature of emacs to capture how long I work on specific tasks.  However from time to time,  I have to aggregate data over several files, on a monthly or yearly basis, and this is where the small tool described here can prove useful. The code and tests for this article may be found [ here ]. One of the tests may be run in SWI-Prolog with those steps:                ?- consult('/path/to/clocking_tool.pl').                true.             ?- test_parse_clock(Start, End, Elapsed).             Start = [2020-2-5, 16:6:0], End = [2020-2-5, 17:26:0], Elapsed = 1:20 ;             false. A version for Tau-Prolog can be found  [he...

Welcome back to this 2 Part introduction to DCGs, more posts are to come. Jumping straight on where Part 1 was left, and in order to understand the inner workings of the conc_sep predicate, one can now: - activate the graphical debugger in the swipl-win tool menu - prepend a "trace, " before the actual DCG test run: ?- trace, test_conc_sep_3(Bird1, Bird2). from that point on my colleague Dr Scratch is taking over and presenting you the steps involved: https://scratch.mit.edu/projects/356943603/     ( duration: 5' ) enjoy !

Introduction Here’s a new series of short articles that concentrate on one powerful tool within Prolog Pr ogramming,   “Definite Clause Grammars”. These are covered in a number of tutorials on the web (refer to the information in the appendix).  However I found a step by step approach, "distilled" with tests, to be the most appropriate learning path, as the topic might otherwise be a bit daunting for newcomers to comprehend. The context where I personally used the technology is for parsing application server logs and parsing programming languages such as Java. A number of probl ems arise when parsing text, such as: the ability to reuse generic structures such as lists and options to structure grammars the ease of capturing the elements recognized by the parser, and maintaining state across several rules (productions) the handling of ambiguous contexts when looking up text tokens (“lookahead”) the handling of rules with left recursion The effectiveness of ...

The previous article presented 2 alternatives for calculating the diff predicates, such as   diff(on(//'NEST', @type), from(//bird, @name)).   using a common strategy for matching objects, and a different strategy for matching sub-nodes of these objects, in the tree_d2_map and tree_d2_lcs implementations respectively.   This approach led however to some code duplication, and thus to the increase of the number of predicates which one might have to write to produce a diff.   The present article now introduces a generic diff implementation that works as a “swiss-army knife”, enabling on-the-spot combinations of node set matching strategies.   Resources for this article Prolog source code and XML examples are available on  [github] , and are linked to this article. To help enhance the readability of the predicates’ output, some Xml elements below are sometimes “ellipsed” with a “…” . A new code structure for decoupling th...

Introduction Building on the previous article I wrote on using the SWI Prolog Xpath predicate for analyzing Xml Node Set relationships, I now describe a way to produce a tree oriented diff based on similar techniques. The goal of such a diff is to identify objects of 2 Xml trees which differ by a given sub-node. In a sense is that diff not a fully general diff, as it focuses on 2 or 3 levels: object sub-or-descendant node resp. property when required, property of the sub-or-descendant node specified by the user, within the Xml tree structure. Another important goal of this diff is to be able to accommodate a different ordering of these objects in the Xml structure, which is normally a constraint which most editors or developer tools can’t cope with. In the following sections I will again use a similar fictitious tree example as in the precedent article. Resources for this article Prolog source code and XML examples are available on  [github] ...

Introduction SWI Prolog provides a Prolog-friendly version of Xpath which consists of defining Xpath expressions as Prolog  terms . The actual API is documented  here . There are a few hurdles which one has to face, coming from using standard Xpath expressions (e.g. with XSLT) and having to transpose them into the Prolog flavor. Having integrated this difference with the standard, one can quickly measure the immense flexibility offered by these Prolog xpath predicates for performing some complex Xml Analysis. Key to this is the possibility to use unification involving some Xml intermediate Node objects, using them as current (local) context nodes, which in Xpath is referred to as the “Axis”. Another concept of Xpath, the NodeSet, can also be covered elegantly by unification. I would like now to showcase this on a small example, using a fictitious tree description, and some imaginary information one would like to extract from it. Resources for ...