From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham autolearn_force=no version=3.4.4 X-Google-Thread: 103376,7728b533f7ab5fb6 X-Google-Attributes: gid103376,domainid0,public,usenet X-Google-Language: ENGLISH,ASCII-7-bit Path: g2news2.google.com!news4.google.com!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail From: "(see below)" Newsgroups: comp.lang.ada Subject: Re: Avoiding side effects Date: Mon, 13 Oct 2008 19:55:17 +0100 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Trace: individual.net P+1hqyz9GOguw8Tpx+ZoIAWoC9jPTCNgK+yrBkRusPT50Mmw9K Cancel-Lock: sha1:65mZNrTnnmcv6lHWv7oZuBMXVpA= User-Agent: Microsoft-Entourage/12.12.0.080729 Thread-Topic: Avoiding side effects Thread-Index: AcktZTuAj4yFzhAY0E+r709/0U9KKQ== Xref: g2news2.google.com comp.lang.ada:8090 Date: 2008-10-13T19:55:17+01:00 List-Id: On 13/10/2008 14:21, in article c3d10577-421a-4fb0-b27f-1395df583dd9@w1g2000prk.googlegroups.com, "Marco" wrote: > On Oct 13, 5:27 am, Anders Wirzenius > wrote: >> "(see below)" writes: >>> On 08/10/2008 06:16, in article u1vyrbra1....@no.email.thanks.invalid, >>> "Anders Wirzenius" wrote: >> >>>> "(see below)" writes: >> >>>>> On 07/10/2008 15:47, in article uprmc4g3i....@no.email.thanks.invalid, >>>>> "Anders Wirzenius" wrote: >> >>>>>> "(see below)" writes: >> >>>>>>> On 07/10/2008 12:08, in article wvbrfxn8hdc7....@sun.com, "Ole-Hjalmar >>>>>>> Kristensen" wrote: >> >>>>>>>> Yes, I think any program which use a read/write interface to a file >>>>>>>> will havesideeffects in that sense. The only way I can think of for >>>>>>>> avoiding this would be to mmap the whole file, then it will appear as >>>>>>>> an array of bytes. >> >>>>>>> Why would stepping through an array not be thought a "side"effect? >> >>>>>> A function that returns the row of that array and only that >>>>>> would perhaps be a function withoutsideeffects. The information >>>>>> in that row can be fetched when needed. >> >>>>> A function that always returns the same row of an array would be of little >>>>> use, I should think. >> >>>> I have a feeling that the function can be programmed so that it returns >>>> different row (numbers, or pointers in that array) depending on >>>> the content of the rows in that array ;-) >> >>>> function Row_Number (Row_Number_In_Other_Array : in >>>> Row_Number_Type) return Row_Number_Type is >>>> -- Return a row number one higher than the row number of the row >>>> -- identical to the row in the other array. >> >>> I think this beautifully illustrates the silliness that slavish adherence to >>> dogma inevitably produces, in programming as in finance and politics. >> >> The thread I started was about how to avoidsideeffects. From >> the answers I have been reading that for a case where you compare >> the content of two files, it is rather hard to do it with >> functions without havingsideeffects. >> >> Is the dogm you refer to something like "functions withoutside >> effects". >> >> I am not a professional programmer any more and I just >> wanted to learn something aboutsideeffects. What is silly in >> that? > > nothing, but I agree don't get carried away with the concept, > Functional Programming is kind of an extreme backlash to the Object > Oriented push of the late 80's and 90's, in the end, both are useful FP started with LISP, ca. 1960, and turned into a major academic industry in the early 1980s. Only AI rivals it as a wholesale waste of CS effort. > but is important to keep as many functions "pure" as possible because > these tend to be easier to verify and are more reusable in other > contexts. > > http://en.wikipedia.org/wiki/Pure_function > > At work, we are trending away from the pure OO stuff to a mixed > approach. -- Bill Findlay chez blueyonder.co.uk