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From |
Jeph Herrin <stata@spandrel.net> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: Why do `test' and a`test' make a difference? |

Date |
Mon, 11 Feb 2013 11:36:25 -0500 |

J On 2/11/2013 10:36 AM, Nick Cox wrote:

I am not aware of a single source that documents in one place how Stata parses command lines. My wild idea is that it would be too complicated or too technical to be of much use, even to programmers. My own main rule is too elementary and too homespun to be much use, namely that it's best to assume that Stata is right by its own rules and that misunderstandings have to be treated by trying to see what you typed from her point of view, token by token, left to right, top down, and very slowly. Nick On Mon, Feb 11, 2013 at 3:01 PM, Jeph Herrin <stata@spandrel.net> wrote:Thanks Daniel and Nick, I can usually work out why I get what I get, or at least get what I want, but do find that my most common programming errors occur because macros do not behave as I anticipate. Clearly, it is a limitation of my intuition, not of Stata, because I don't doubt that Stata is consistent; and I also don't doubt that if I used Stata for parsing strings as much as I once used Perl or awk or sed (ie, many hours a day) I wouldn't be surprised so often. Still, that I still get bit by these - and Stata is practically the only thing I program these last few years - suggests that the quirkiness Nick refers is perhaps a bit overglossed. cheers, Jeph On 2/11/2013 8:24 AM, Nick Cox wrote:Daniel's excellent, thorough answer is difficult to gloss. Cory's elegant summary "Stata kinda sucks with strings..." is, however, I think a little hard and so some more general comments seem in order. Every programming or command language of substance faces a challenge that once you give specific syntactic meaning to certain characters, then you make it more difficult to use those characters with their standard, customary or literal meanings. Also, you may get bitten by forgetting or not knowing about the difference. (Me too, naturally.) Also, programmers in my experience tend to get accustomed to the particular choices made in a certain language and then are inclined to regard other solutions in other languages as defective or at least strange. Stata is quirky in wanting to interpret `stuff' as a reference to a local macro named stuff. Extensions of that syntax `: ' and `= ' may seem equally strange. So, that can get complicated when you want either or both single quotation marks for other purposes. The original syntax for local macro references was fairly ugly %_stuff was a reference to what was defined by mac def _stuff "some stuff" You can still use that under version control! Nick On Mon, Feb 11, 2013 at 11:53 AM, daniel klein <klein.daniel.81@gmail.com> wrote:As for Jeph's request for a systematic account of how word lists are parsed, I think this is explained in the manuals and is more about macro expansion than lists of words. When you type `: word 1 of `test'' Stata sees `: word 1 of Jeph's Example' since `: word 1 of Jeph' expands to Jeph, you get Jephs Example' When you type : word 1 of `test' Stata sees : word 1 of Jeph's Example which expands to Jeph's When you type `"`:word 1 of `test''"'+"[ ]"+`"`:word 2 of `test''"' Stata sees `"`: word 1 of Jeph's Example'"' + "[]" + `"`: word 2 of Jeph's Example'"'' we already coverd the first part of this, so lets take a look on the second. Since `: word 2 of Jeph' is an empty string teh hole expression becomes `"Jephs Example'[]s Example'"' These outputs might not be what you want, but exactly what you would expect following Stata's logic of macro expansion. Thre is nothing unsensical or mysterious about it. Best Daniel -- It's getting tripped up by the apostrophe in test since it's a character with special meaning. Stata kinda sucks with strings... Try local test "Jephs Example" and it will be more sensical. On Sun, Feb 10, 2013 at 10:10 PM, Jeph Herrin <stata@spandrel.net> wrote:I'd like a systematic account of how word lists are parsed. For instance, I have been scratching my head over the output of this: local test "Jeph's Example" local wordA `: word 1 of `test'' local wordB : word 1 of `test' local wordC =`"`:word 1 of `test''"'+"[ ]"+`"`:word 2 of `test''"' di "`wordA'" di "`wordB'" di "`wordC'"* * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/* * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/* * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

**References**:**Re: st: Why do `test' and a`test' make a difference?***From:*daniel klein <klein.daniel.81@gmail.com>

**Re: st: Why do `test' and a`test' make a difference?***From:*Nick Cox <njcoxstata@gmail.com>

**Re: st: Why do `test' and a`test' make a difference?***From:*Jeph Herrin <stata@spandrel.net>

**Re: st: Why do `test' and a`test' make a difference?***From:*Nick Cox <njcoxstata@gmail.com>

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