Related
I have met this a lot recently reading other people's scripts. A short example is below:
Say we need input and store them in var A and B, the scheme is below:
int ok;
ok = false;
while(!ok){
//ask input for A
//ask input for B
ok = true;
}
I understand what it wants, but why is this scheme necessary? can I only have "ask input for A and B".
but why is this scheme necessary?
It is not necessary.
can I only have "ask input for A and B".
You sure can.
However, if user gives you input that is not useful (for example: you ask for the users age, and they type "horse"), then you might want to ask again. Allowing re-trying of input is generally a useful feature. The canonical control structure for repeating a piece of program is a loop.
Your example program however, sets ok unconditionally, so in that case there is really no use for the loop. The loop makes sense only if there is some form of validation that must be passed before the input is OK.
When there are no checks in the code you omitted, but you see this same construct all over the place, then it's a copy&paste artifact.
Someone had a piece of code that was reading input and validating it, then copied the code somewhere else, removed the validation bits, and left the rest as-is. Then they copy&pasted that code all over the place.
In my experience, this happens very often.
I didn't touch Prolog since high-school, and even though I've tried to find the info, it didn't help. Below is the example that has to illustrate my problem:
%% everybody():- [dana, cody, bess, abby].
%% Everybody = [dana, cody, bess, abby].
likes(dana, cody).
hates(bess, dana).
hates(cody, abby).
hates(X, Y):- \+ likes(X, Y).
likes_somebody(_, []):- fail.
likes_somebody(X, [girl | others]):-
likes(X, girl) ; likes_somebody(X, others).
likes_everybody(_, []):- true.
likes_everybody(X, [girl | others]):-
likes(X, girl) , likes_everybody(X, others).
maplist(likes_somebody, [dana, cody, bess, abby], [dana, cody, bess, abby]).
How do I declare everybody to just be the list of girls? The commented lines are those which I've tried, but I've got bizarre error messages back.
This is the tutorial I followed more or less so far. I'm using GProlog, if it makes any difference. Sorry for such a basic question. GProlog's manual doesn't deal with language syntax, but I've certainly looked there. As an aside, I would be grateful for information on where to look for language documentation (as opposed to implementation documentation).
Every variable in Prolog must begin with an uppercase letter. So for starters, you want Everybody, not everybody.
Second problem, variables in Prolog are not assignables. So probably what you want to do is make a fact and use that instead:
everybody([dana, cody, bess, abby]).
Your bottom line of code is actually a fact definition and will attempt to overwrite maplist/3. What you probably want to do is put everything above that line into a file (say, called likes.pl) and then consult it ([likes].). Then you can run a query like this:
?- everybody(Everybody), maplist(likes_somebody, Everybody, Everybody).
This won't work, because likes_somebody/2 processes a list in the second argument. The predicate you have for likes_somebody/2 could be written:
likes_somebody(_, []).
but still won't mean much. It simply unifies anything with the empty list:
?- likes_somebody(chicken_tacos, []).
true.
You really need a predicate to tell you if someone is a girl, like this:
girl(dana).
girl(cody).
girl(bess).
girl(abby).
Then you could do what I think you're trying to do, which is something closer to this:
likes_somebody(X) :- girl(X).
Then the maplist construction would work like this:
everybody(Everybody), maplist(likes_somebody, Everybody).
Which would simply return true. You could simplify and eliminate everybody/1 by instead using findall(Girl, girl(X), Everybody) but it's getting weird.
You're trying to do list processing with likes_everybody/2, but it's broken because girl is literally girl, not a variable, and others is literally others, not a list of some kind that could be the tail of another list.
I think you still have some old ideas you need to cleanse. Read some more, write some more, and your code will start to make a lot more sense.
This might be an odd question, but I'm looking for a word to use in a function name. I'm normally good at coming up with succinct, meaningful function names, but this one has me stumped so I thought I'd appeal for help.
The function will take some desired state as an argument and compare it to the current state. If no change is needed, the function will exit normally without doing anything. Otherwise, the function will take some action to achieve the desired state.
For example, if wanted to make sure the front door was closed, i might say:
my_house.<something>_front_door('closed')
What word or term should use in place of the something? I'd like it to be short, readable, and minimize the astonishment factor.
A couple clarifying points...
I would want someone calling the function to intuitively know they didn't need to wrap the function an 'if' that checks the current state. For example, this would be bad:
if my_house.front_door_is_open():
my_house.<something>_front_door('closed')
Also, they should know that the function won't throw an exception if the desired state matches the current state. So this should never happen:
try:
my_house.<something>_front_door('closed')
except DoorWasAlreadyClosedException:
pass
Here are some options I've considered:
my_house.set_front_door('closed')
my_house.setne_front_door('closed') # ne=not equal, from the setne x86 instruction
my_house.ensure_front_door('closed')
my_house.configure_front_door('closed')
my_house.update_front_door('closed')
my_house.make_front_door('closed')
my_house.remediate_front_door('closed')
And I'm open to other forms, but most I've thought of don't improve readability. Such as...
my_house.ensure_front_door_is('closed')
my_house.conditionally_update_front_door('closed')
my_house.change_front_door_if_needed('closed')
Thanks for any input!
I would use "ensure" as its succinct, descriptive and to the point:
EnsureCustomerExists(CustomerID)
EnsureDoorState(DoorStates.Closed)
EnsureUserInterface(GUIStates.Disabled)
Interesting question!
From the info that you have supplied, it seems to me that setstate (or simply set, if you are setting other things than states) would be fine, though ensure is good if you want to really emphasize the redundancy of an if.
To me it is however perfectly intuitive that setting a state does not throw an exception, or require an if. Think of setting the state of any other variable:
In C:
int i;
i = 5; // Would you expect this to throw an exception if i was already 5?
// Would you write
if (i != 5)
i = 5;
// ?
Also it only takes about one sentence to document this behaviour:
The function does nothing if the
current state equals the requested
state.
EDIT: Actually, thinking about it, if it is really important to you (for some reason) that the user is not confused about this, I would in fact pick ensure (or some other non-standard name). Why? Because as a user, a name like that would make me scratch my head a bit and look up the documentation ("This is more than just an ordinary set-function, apparently").
EDIT 2: Only you know how you design your programs, and which function name fits in best. From what you are saying, it seems like your setting functions sometimes throw exceptions, and you need to name a setting function that doesn't - e.g. set_missile_target. If that is the case, I think you should consider the set_if, set_when, set_cond or cond_set names. Which one would kind of depend on the rest of your code. I would also add that one line of documentation (or two, if you're generous), which clarifies the whole thing.
For example:
// Sets missile target if current target is not already the requested target,
// in which case it does nothing. No exceptions are thrown.
function cond_set_missile_target ()
or function cond_set_MissileTarget ()
or function condSet_MissileTarget ()
or function condSetMissileTarget ()
ensure is not so bad, but to me it implies only that there is additional logic required to set the state (e.g. multiple states tied together, or other complications). It helps to make the user avoid adding unnecessary ifs, but it does not help much with the exception issue. I would expect an ensure function to throw an exception sooner than a set function, since the ensure function clearly has more responsibilities for, well, ensuring that this setting operation is in fact done right.
I'd go for ensure for the function you describe. I'd also use camelCase, but I suppose you may be in a language that prefers underscores.
You could always document (shock!) your API so that others don't make the mistakes you describe.
Hey guys, given a data set in plain text such as the following:
==Events==
* [[312]] – [[Constantine the Great]] is said to have received his famous [[Battle of Milvian Bridge#Vision of Constantine|Vision of the Cross]].
* [[710]] – [[Saracen]] invasion of [[Sardinia]].
* [[939]] – [[Edmund I of England|Edmund I]] succeeds [[Athelstan of England|Athelstan]] as [[King of England]].
*[[1275]] – Traditional founding of the city of [[Amsterdam]].
*[[1524]] – [[Italian Wars]]: The French troops lay siege to [[Pavia]].
*[[1553]] – Condemned as a [[Heresy|heretic]], [[Michael Servetus]] is [[burned at the stake]] just outside [[Geneva]].
*[[1644]] – [[Second Battle of Newbury]] in the [[English Civil War]].
*[[1682]] – [[Philadelphia]], [[Pennsylvania]] is founded.
I would like to end up with an NSDictionary or other form of collection so that I can have the year (The Number on the left) mapping to the excerpt (The text on the right). So this is what the 'template' is like:
*[[YEAR]] – THE_TEXT
Though I would like the excerpt to be plain text, that is, no wiki markup so no [[ sets. Actually, this could prove difficult with alias links such as [[Edmund I of England|Edmund I]].
I am not all that experienced with regular expressions so I have a few questions. Should I first try to 'beautify' the data? For example, removing the first line which will always be ==Events==, and removing the [[ and ]] occurrences?
Or perhaps a better solution: Should I do this in passes? So for example, the first pass I can separate each line into * [[710]] and [[Saracen]] invasion of [[Sardinia]]. and store them into different NSArrays.
Then go through the first NSArray of years and only get the text within the [[]] (I say text and not number because it can be 530 BC), so * [[710]] becomes 710.
And then for the excerpt NSArray, go through and if an [[some_article|alias]] is found, make it only be [[alias]] somehow, and then remove all of the [[ and ]] sets?
Is this possible? Should I use regular expressions? Are there any ideas you can come up with for regular expressions that might help?
Thanks! I really appreciate it.
EDIT: Sorry for the confusion, but I only want to parse the above data. Assume that that's the only type of markup that I will encounter. I'm not necessarily looking forward to parsing wiki markup in general, unless there is already a pre-existing library which does this. Thanks again!
This code assumes you are using RegexKitLite:
NSString *data = #"* [[312]] – [[Constantine the Great]] is said to have received his famous [[Battle of Milvian Bridge#Vision of Constantine|Vision of the Cross]].\n\
* [[710]] – [[Saracen]] invasion of [[Sardinia]].\n\
* [[939]] – [[Edmund I of England|Edmund I]] succeeds [[Athelstan of England|Athelstan]] as [[King of England]].\n\
*[[1275]] – Traditional founding of the city of [[Amsterdam]].";
NSString *captureRegex = #"(?i)(?:\\* *\\[\\[)([0-9]*)(?:\\]\\] \\– )(.*)";
NSRange captureRange;
NSRange stringRange;
stringRange.location = 0;
stringRange.length = data.length;
do
{
captureRange = [data rangeOfRegex:captureRegex inRange:stringRange];
if ( captureRange.location != NSNotFound )
{
NSString *year = [data stringByMatching:captureRegex options:RKLNoOptions inRange:stringRange capture:1 error:NULL];
NSString *textStuff = [data stringByMatching:captureRegex options:RKLNoOptions inRange:stringRange capture:2 error:NULL];
stringRange.location = captureRange.location + captureRange.length;
stringRange.length = data.length - stringRange.location;
NSLog(#"Year:%#, Stuff:%#", year, textStuff);
}
}
while ( captureRange.location != NSNotFound );
Note that you really need to study up on RegEx's to build these well, but here's what the one I have is saying:
(?i)
Ignore case, I could have left that out since I'm not matching letters.
(?:\* *\[\[)
?: means don't capture this block, I escape * to match it, then there are zero or more spaces (" *") then I escape out two brackets (since brackets are also special characters in a regex).
([0-9]*)
Grab anything that is a number.
(?:\]\] \– )
Here's where we ignore stuff again, basically matching " – ". Note any "\" in the regex, I have to add another one to in the Objective-C string above since "\" is a special character in a string... and yes that means matching a regex escaped single "\" ends up as "\\" in an Obj-C string.
(.*)
Just grab anything else, by default the RegEX engine will stop matching at the end of a line which is why it doesn't just match everything else. You'll have to add code to strip out the [[LINK]] stuff from the text.
The NSRange variables are used to keep matching through the file without re-matching original matches. So to speak.
Don't forget after you add the RegExKitLite class files, you also need to add the special linker flag or you'll get lots of link errors (the RegexKitLite site has installation instructions).
I'm no good with regular expressions, but this sounds like a job for them. I imagine a regex would sort this out for you quite easily.
Have a look at the RegexKitLite library.
If you want to be able to parse Wikitext in general, you have a lot of work to do. Just one complicating factor is templates. How much effort do you want to go to cope with these?
If you're serious about this, you probably should be looking for an existing library which parses Wikitext. A brief look round finds this CPAN library, but I have not used it, so I can't cite it as a personal recommendation.
Alternatively, you might want to take a simpler approach and decide which particular parts of Wikitext you're going to cope with. This might be, for example, links and headings, but not lists. Then you have to focus on each of these and turn the Wikitext into whatever you want that to look like. Yes, regular expressions will help a lot with this bit, so read up on them, and if you have specific problems, come back and ask.
Good luck!
I would really like to see a proportional font IDE, even if I have to build it myself (perhaps as an extension to Visual Studio). What I basically mean is MS Word style editing of code that sort of looks like the typographical style in The C++ Programming Language book.
I want to set tab stops for my indents and lining up function signatures and rows of assignment statements, which could be specified in points instead of fixed character positions. I would also like bold and italics. Various font sizes and even style sheets would be cool.
Has anyone seen anything like this out there or know the best way to start building one?
I'd still like to see a popular editor or IDE implement elastic tabstops.
Thinking with Style suggests to use your favorite text-manipulation software like Word or Writer. Create your programme code in rich XML and extract the compiler-relevant sections with XSLT. The "Office" software will provide all advanced text-manipulation and formatting features.
i expected you'll get down-modded and picked on for that suggestion, but there's some real sense to the idea.
The main advantage of the traditional 'non-proportional' font requirement in code editors is to ease the burden of performing code formatting.
But with all of the interactive automatic formatting that occurs in modern IDE's, it's really possible that a proportional font could improve the readability of the code (rather than hampering it, as i'm sure many purists would expect).
A character called Roedy Green (famous for his 'how to write unmaintainable code' articles) wrote about a theoretical editor/language, based on Java and called Bali. It didn't include non-proportional fonts exactly, but it did include the idea of having non-uniform font-sizes.
Also, this short Joel Spolsky post posts to a solution, elastic tab stops (as mentioned by another commentor) that would help with the support of non-proportional (and variable sized) fonts.
#Thomas Owens
I don't find code formatted like that easier to read.
That's fine, it is just a personal preference and we can disagree. Format it the way you think is best and I'll respect it. I frequently ask myself 'how should I format this or that thing?' My answer is always to format it to improve readability, which I admit can be subjective.
Regarding your sample, I just like having that nicely aligned column on the right hand side, its sort of a quick "index" into the code on the left. Having said that, I would probably avoid commenting every line like that anyway because the code itself shouldn't need that much explanation. And if it does I tend to write a paragraph above the code.
But consider this example from the original poster. Its easier to spot the comments in the second one in my opinion.
for (size-type i = 0; i<v.size(); i++) { // rehash:
size-type ii = has(v[i].key)%b.size9); // hash
v[i].next = b[ii]; // link
b[ii] = &v[i];
}
for (size-type i = 0; i<v.size(); i++) { // rehash:
size-type ii = has(v[i].key)%b.size9); // hash
v[i].next = b[ii]; // link
b[ii] = &v[i];
}
#Thomas Owens
But do people really line comments up
like that? ... I never try to
line up declarations or comments or
anything, and the only place I've ever
seen that is in textbooks.
Yes people do line up comments and declarations and all sorts of things. Consistently well formatted code is easier to read and code that is easier to read is easier to maintain.
I wonder why nobody actually answers your question, and why the accepted answer doesn't really have anything to do with your question. But anyway...
a proportional font IDE
In Eclipse you can cchoose any font on your system.
set tab stops for my indents
In Eclipse you can configure the automatic indentation, including setting it to "tabs only".
lining up function signatures and rows of assignment statements
In Eclipse, automatic indentation does that.
which could be specified in points instead of fixed character positions.
Sorry, I don't think Eclipse can help you there. But it is open source. ;-)
bold and italics
Eclipse has that.
Various font sizes and even style sheets would be cool
I think Eclipse only uses one font and font-size for each file type (for example Java source file), but you can have different "style sheets" for different file types.
When I last looked at Eclipse (some time ago now!) it allowed you to choose any installed font to work in. Not so sure whether it supported the notion of indenting using tab stops.
It looked cool, but the code was definitely harder to read...
Soeren: That's kind of neat, IMO. But do people really line comments up like that? For my end of line comments, I always use a single space then // or /* or equivalent, depending on language I'm using. I never try to line up declarations or comments or anything, and the only place I've ever seen that is in textbooks.
#Brian Ensink: I don't find code formatted like that easier to read.
int var1 = 1 //Comment
int longerVar = 2 //Comment
int anotherVar = 4 //Command
versus
int var2 = 1 //Comment
int longerVar = 2 //Comment
int anotherVar = 4 //Comment
I find the first lines easier to read than the second lines, personally.
The indentation part of your question is being done today in a real product, though possibly to even a greater level of automation than you imagined, the product I mention is an XSLT IDE, but the same formatting principles would work with most (but not all) conventional code syntaxes.
This really has to be seen in video to get the sense of it all (sorry about the music back-track). There's also a light XML editor spin-off product, XMLQuire, that serves as a technology demonstrator.
The screenshot below shows XML formatted with quite complex formatting rules in this XSLT IDE, where all indentation is performed word-processor style, using the left margin - not space or tab characters.
To emphasise this formatting concept, all characters have been highlighted to show where the left-margin extends to keep indentation. I use the term Virtual Formatting to describe this - it's not like elastic tab stops, because there simply are no tabs, just margin information which is part of the 'paragraph' formatting (RTF codes are used here). The parser reformats continuously, in the same pass as syntax coloring.
A proportional font hasn't been used here, but it could have been quite easily - because the indentation is set in TWIPS. The editing experience is quite compelling because, as you refactor the code (XML in this case), perhaps through drag and drop, or by extending the length of an attribute value, the indentation just re-flows itself to fit - there's no tab-key or 'reformat' button to press.
So, the indentation is there, but the font work is a more complex problem. I've experimented with this, but found that if fonts are re-selected as you type, the horizontal shifting of the code is too distracting - there would need to be a user-initiated 'format fonts' command probably. The product also has Ink/Handwriting technology built-in for annotating code, but I've yet to exploit this in the live release.
Folks are all complaining about comments not lining up.
Seems to me that there's a very simple solution: Define the unit space as the widest character in the font. Now, proportionally space all characters except the space. the space takes up as much room so as to line up the next character where it would be if all preceeding characters on the line were the widest in the font.
ie:
iiii_space_Foo
xxxx_space_Foo
would line up the "Foo", with the space after the "i" being much wider than after the "x".
So call it elastic spaces. rather than tab-stops.
If you're a smart editor, treat comments specially, but that's just gravy
Let me recall arguments about using the 'var' keyword in C#. People hated it, and thought it would make code less clear. For example, you couldn't know the type in something like:
var x = GetResults("Main");
foreach(var y in x)
{
WriteResult(x);
}
Their argument was, that you couln't see if x was an array, an List or any other IEnumerable. Or what the type of y was. In my opinion the unclearity did not arise from using var, but from picking unclear variable names. Why not just type:
var electionResults = GetRegionalElactionResults("Main");
foreach(var result in electionResults)
{
Write(result); // you can see what you're writing!!
}
"But you still cannot see the type of electionResults!" - does it really matter? If you want to change the return type of GetRegionalElectionResults, you can do so. Any IEnumerable will do.
Fast forward to now. People want to align comments en similar code:
int var2 = 1; //The number of days since startup, including the first
int longerVar = 2; //The number of free days per week
int anotherVar = 38; //The number of working hours per week
So without the comment everything is unclear. And if you don't align the values, you cannot seperate them from the variales. But do you? What about this (ignore the bullets please)
int daysSinceStartup = 1; // including first
int freeDaysPerWeek = 2;
int workingHoursPerWeek = 38;
If you need a comment on EVERY LINE, you're doing something wrong. "But you still need to align the VALUES" - do you? what does 38 have to do with 2?
In C# Most code blocks can easily be aligned using only tabs (or acually, multiples of four spaces):
var regionsWithIncrease =
from result in GetRegionalElectionResults()
where result.TotalCount > result > PreviousTotalCount &&
result.PreviousTotalCount > 0 // just new regions
select result.Region;
foreach (var region in regionsWithIncrease)
{
Write(region);
}
You should never use line-to-line comments and you should rarely need to vertically align things. Rarely, not never. So I understand if some of you guys prefer a monospaced font. I prefer the readibility of font Noto Sans or Source Sans Pro. These fonts are available freely from Google, and resemble Calibri, but are designed for programming and thus have all the neccesary characteristics:
Big : ; . , so you can clearly see the difference
Clearly distinct 0Oo and distinct Il|
The major problem with proportional fonts is they destroy the vertical alignment of the code and this is a fairly major loss when it comes to writing code.
The vertical alignment makes it possible to manipulate rectangular blocks of code that span multiple lines by allowing block operations like cut, copy, paste, delete and indent, unindent etc to be easily performed.
As an example consider this snippet of code:
a1 = a111;
B2 = aaaa;
c3 = AAAA;
w4 = wwWW;
W4 = WWWW;
In a mono-spaced font the = and the ; all line up.
Now if this text is loded into Word and display using a proportional font the text effectively turns into this:
NOTE: Extra white space added to show how the = and ; no longer line up:
a1 = a1 1 1;
B2 = aaaa;
c3 = A A A A;
w4 = w w W W;
W4 = W W W W;
With the vertical alignment gone those nice blocks of code effectively disappear.
Also because the cursor is no longer guaranteed to move vertically (i.e. the column number is not always constant from one line to the next) it makes it more difficult to write throw away macro scripts designed to manipulated similar looking lines.