Showing posts with label DEF. Show all posts
Showing posts with label DEF. Show all posts

Tuesday, January 08, 2008

[Protium] Master Class #1 (Part 2)

Demonstration - Oblique Strategies

"The Oblique Strategies are a deck of cards. Up until 1996, they were quite easy to describe. They measured about 2-3/4" x 3-3/4". They came in a small black box which said "OBLIQUE STRATEGIES" on one of the top's long sides and "BRIAN ENO/PETER SCHMIDT" on the other side. The cards were solid black on one side, and had the aphorisms printed in a 10-point sans serif face on the other.

...

The deck itself had its origins in the discovery by Brian Eno that both he and his friend Peter Schmidt ... tended to keep a set of basic working principles which guided them through the kinds of moments of pressure — either working through a heavy painting session or watching the clock tick while you're running up a big buck studio bill. Both Schmidt and Eno realized that the pressures of time tended to steer them away from the ways of thinking they found most productive when the pressure was off. The Strategies were, then, a way to remind themselves of those habits of thinking — to jog the mind."         
-- Oblique Strategies
A web-based installation of Oblique Strategies is supplied in the standard Protium install. Using the "Internet Information Services" snap-in, create a virtual directory pointing to C:\protium\Code\prx\os. Specify its default as index.prx, call it 'os', and share the C:\protium\Code\prx\os directory (Microsoft Access is picky about being able to write to databases even when only reading.)

Further information on setting up IIS can be found in the Protium document "C:\protium\bin\plugins\Configuring Windows IIS 5 to use with Protium and Isis.html"

The Protium code in the index.prx file is as follows:
The above code (indented only to more clearly demonstrate document structure) outputs a different strategy each time the page is refreshed. The syllables translate as follows:
<@ DEFKEYLIT>__Transput|__HTMLTransput</@>define the Transput as HTML
<@ SAYPRO>output a document prologue. (What is output by the PRO syllable depends on the Transput defined, as is the case for all document related syllables.)
<@ SAYDOC>Enclose a document.
<@ SAYDHD>Enclose a document header, in the context of an existing document.
<@ SAYDTT>Oblique strategies</@>set the document title, in the context of an existing document body and header.
<@ SAYDBD></@>enclose a document body, in the context of an existing document.
<@ DEFDBFLIT>os</@>opens this data source, by default a JET/MSAccess database.
<@ DEFRSTCAP>select * from os where cardid = <@ SAYRANLIT>100</@></@>Open record source defined by captured output.
<@ SAYRANLIT>100</@>return a random number between 1 and 100.
<@ SAYDPR></@>enclose a document paragraph, in the context of the existing document.
<@ SAYFLD>message</@>print the contents of the field called 'message' which, in this context, is part of the 'os' recordset.
Note that the code chooses a strategy based on a random number between 1 and 100. But what if there are more than 100 strategies? Wouldn't it be better if the actual number of records could be found and that used as the basis for the RAN syllable? Two ways of handling this requirement are described below:

The changed syllables translate as follows:
<@ DEFRSTLIT>os</@>Select every record in the database.
<@ LETVARSZERST>upper|___</@>assign to the variable 'upper' the size of the default (marked by three underscores) recordset.
<@ RSTCAP>select * from os where cardid = <@ SAYRANVAR>upper</@></@>Select a new recordset, capturing the output from RAN but using the variable 'upper' to specify the limit.
Rather than get the number of records, simply ...
<@ ACTMOVRANRST></@>move the record pointer to a random place in the recordset.
This demonstrates the power of idiomatic Protium: short, sweet and to the point.

Questions and Answers

I can't see a main() anywhere. Where's the start?

Protium implements a single-pass code evaluation model. This is quite unlike most other languages which implement double-pass code evaluation: first pass to discover and make a map; second pass to evaluate.

Protium starts at the beginning of a named file, and builds its awareness of context from there. Because of this approach, we may never examine code we aren't interested in.

I keep using the same construction over and over again. Is there a way of abbreviating Protium words?

What you can do is create a compound operator (a concept borrowed from OPS-3). These are defined using the KOP syllable. If you wanted to define LVK as a shorthand for LETVARKEY, for example, then you would code


Thereafter you would be able to use the abbreviated form, replacing code like
with


There are other ways of doing this, including UDS (user-defined syllable) and BLK (code block), but this is by far the simplest.

*** End of Part 2 ***


© Copyright Bruce M. Axtens, 2008
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Saturday, September 08, 2007

[Protium] 'Assert' as a User-Defined Syllable (UDS)

From time to time, during development, it helps to have an assert. That is, a means of checking whether you got the answer you were expecting, but without having to write lots of repetitive code in the process. To that end, therefore, I've come up with a UDS, an user defined syllable, which implements the concept (and demonstrates other Protium functionality as well.)

For the sake of clarity, I've put each syllable, or "opcode", in title case. This is not something that must be done; Protium cares not what case or mix of cases the instructions are in.
A UDS is 'defined', thus the DEF at the beginning. An UDS has 3 parameters: the syllable itself, then the kind of UDS (more about that later), and then the Protium code which is processed each time the syllable is used. In this case, the syllable is ASR, the type is '__Transformer' and the code starts with <@ SAO> (more about SAO later, too).

Parameters may be passed to UDSes, and retrieved using PAR. In this case, the variable lhs is given the value of the first parameter, and the variable rhs the value of the second.

Next comes the test which forms the basis of an assert: does what is contained in lhs equal what is contained in rhs? The fourth line's opcodes implement this test: if not exact-match variable variable literal, with the arguments lhs, rhs and then another Protium instruction which is only evaluated if the test for exact-match fails.

If lhs does not match rhs, an EKM (Expand Macro Key And Memory) of the literal string "Assertion error: '&lhs;' <> '&rhs;'" is performed. lhs and rhs are bracketed by ampersand and comma, with the result that these symbols are replaced with the values of the variables themselves. The result is stored in the RES (the result) of the UDS, which is handed back to the calling code. Next comes a block wrapped in IGN. This is an artefact from the development of ASR. Code inside an IGN is ignored, that is, not executed. IGNs are predominantly used for documentation but can just as easily be used to isolate parts of the code.
Here are two invocations of the ASR syllable. The first generates nothing because the actioned RMD, the reverse-mid, actually does convert "Once a jolly swagman camped by a billabong" into "Once a jolly squatter camped by a billabong". The second invocation gives the error message because there's no way that that reverse-mid is going to be able to produce "all your base are belong to us".

Now SAO, aside from being the name of an Arnott's biscuit, also stands for "Suppress All Output". Usually text outside the <@> and </@> of a Protium instruction is echoed to the relevant transput (read input-output device). SAO suppresses that echoing. This explains why you don't see 'lhs=' and 'rhs=' each time ASR is invoked. SAO also suppresses everything output by SAY.

Regarding __Transformer, every syllable opcode belongs to a particular group of syllables and each group has certain specific behaviours. Other groups include __Modifier, __Alternator, __Evaluator and __Locator. Read the friendly manual.

Finally, a word about testing. It was the developer's original design to separate testing from branching, and it was due to pressure from the Protium user community which forced the merging of the two into the form seen in most other programming languages. According to the original design, the test and branch code should have looked like this:
Both ways of doing it work. I'm starting to come round to the idea that the original design is the better one, especially seeing that Protium supports ternary logic (true, false, unknown). More about that some other time.

This article can also be found at Isotopes of Hydrogen on the Protium Blue Forum.

© Copyright Bruce M. Axtens, 2007

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