Related
I assume it doesn't.
My reason is that Haskell is pure functional programming (without I/O Monad), they could have made every "call by name" use the same evaluated value if the "name"s are the same.
I don't know anything about the implementation details but I'm really interested.
Detailed explanations will be much appreciated :)
BTW, I tried google, it was quite hard to get anything useful.
First of all, Haskell is a specification, not an implementation; the report does not actually require use of call-by-name evaluation, or lazy evaluation for that matter. Haskell implementations are only required to be non-strict, which does rule out call-by-value and similar strategies.
So, strictly (ha, ha) speaking, evaluation strategies can't slow down Haskell. I'm not sure what can slow down Haskell, though clearly something has or else it wouldn't have taken 12 years to get the next version of the Report out after Haskell 98. My guess is that it involves committees somehow.
Anyway, "lazy evaluation" refers to a "call by need" strategy, which is the most common implementation choice for Haskell. This differs from call-by-name in that if a subexpression is used in multiple places, it will be evaluated at most once.
The details of what qualifies as a subexpression that will be shared is a bit subtle and probably somewhat implementation-dependent, but to use an example from GHC Haskell: Consider the function cycle, which repeats an input list infinitely. A naive implementation might be:
cycle xs = xs ++ cycle xs
This ends up being inefficient because there is no single cycle xs expression that can be shared, so the resulting list has to be constructed continually as it's traversed, allocating more memory and doing more computation each time.
In contrast, the actual implementation looks like this:
cycle xs = xs' where xs' = xs ++ xs'
Here the name xs' is defined recursively as itself appended to the end of the input list. This time xs' is shared, and evaluated only once; the resulting infinite list is actually a finite, circular linked list in memory, and once the entire loop has been evaluated no further work is needed.
In general, GHC will not memoize functions for you: given f and x, each use of f x will be re-evaluated unless you give the result a name and use that. The resulting value will be the same in either case, but the performance can differ significantly. This is mostly a matter of avoiding pessimizations--it would be easy for GHC to memoize things for you, but in many cases this would cost large amounts of memory to gain tiny or nonexistent amounts of speed.
The flip side is that shared values are retained; if you have a data structure that's very expensive to compute, naming the result of constructing it and passing that to functions using it ensures that no work is duplicated--even if it's used simultaneously by different threads.
You can also pessimize things yourself this way--if a data structure is cheap to compute and uses lots of memory, you should probably avoid sharing references to the full structure, as that will keep the whole thing alive in memory as long as anything could possibly use it later.
Yes, it does, somewhat. The problem is that Haskell can't, in general, calculate the value too early (e.g. if it would lead to an exception), so it sometimes needs to keep a thunk (code for calculating the value) instead of the value itself, which uses more memory and slows things down. The compiler tries to detect cases where this can be avoided, but it's impossible to detect all of them.
I’m taking my first baby-steps in learning functional programing using F# and I’ve just come across the Forward Pipe (|>) and Forward Composition (>>) operators. At first I thought they were just sugar rather than having an effect on the final running code (though I know piping helps with type inference).
However I came across this SO article:
What are advantages and disadvantages of “point free” style in functional programming?
Which has two interesting and informative answers (that instead of simplifying things for me opened a whole can of worms surrounding “point-free” or “pointless” style) My take-home from these (and other reading around) is that point-free is a debated area. Like lambas, point-free style can make code easier to understand, or much harder, depending on use. It can help in naming things meaningfully.
But my question concerns a comment on the first answer:
AshleyF muses in the answer:
“It seems to me that composition may reduce GC pressure by making it more obvious to the compiler that there is no need to produce intermediate values as in pipelining; helping make the so-called "deforestation" problem more tractable.”
Gasche replies:
“The part about improved compilation is not true at all. In most languages, point-free style will actually decrease performances. Haskell relies heavily on optimizations precisely because it's the only way to make the cost of these things bearable. At best, those combinators are inlined away and you get an equivalent pointful version”
Can anyone expand on the performance implications? (In general and specifically for F#) I had just assumed it was a writing-style thing and the compiler would unstrangle both idioms into equivalent code.
This answer is going to be F#-specific. I don't know how the internals of other functional languages work, and the fact that they don't compile to CIL could make a big difference.
I can see three questions here:
What are the performance implications of using |>?
What are the performance implications of using >>?
What is the performance difference between declaring a function with its arguments and without them?
The answers (using examples from the question you linked to):
Is there any difference between x |> sqr |> sum and sum (sqr x)?
No, there isn't. The compiled CIL is exactly the same (here represented in C#):
sum.Invoke(sqr.Invoke(x))
(Invoke() is used, because sqr and sum are not CIL methods, they are FSharpFunc, but that's not relevant here.)
Is there any difference between (sqr >> sum) x and sum (sqr x)?
No, both samples compile to the same CIL as above.
Is there any difference between let sumsqr = sqr >> sum and let sumsqr x = (sqr >> sum) x?
Yes, the compiled code is different. If you specify the argument, sumsqr is compiled into a normal CLI method. But if you don't specify it, it's compiled as a property of type FSharpFunc with a backing field, whose Invoke() method contains the code.
But the effect of all is that invoking the point-free version means loading one field (the FSharpFunc), which is not done if you specify the argument. But I think that shouldn't measurably affect performance, except in the most extreme circumstances.
Like lots of you guys on SO, I often write in several languages. And when it comes to planning stuff, (or even answering some SO questions), I actually think and write in some unspecified hybrid language. Although I used to be taught to do this using flow diagrams or UML-like diagrams, in retrospect, I find "my" pseudocode language has components of C, Python, Java, bash, Matlab, perl, Basic. I seem to unconsciously select the idiom best suited to expressing the concept/algorithm.
Common idioms might include Java-like braces for scope, pythonic list comprehensions or indentation, C++like inheritance, C#-style lambdas, matlab-like slices and matrix operations.
I noticed that it's actually quite easy for people to recognise exactly what I'm triying to do, and quite easy for people to intelligently translate into other languages. Of course, that step involves considering the corner cases, and the moments where each language behaves idiosyncratically.
But in reality, most of these languages share a subset of keywords and library functions which generally behave identically - maths functions, type names, while/for/if etc. Clearly I'd have to exclude many 'odd' languages like lisp, APL derivatives, but...
So my questions are,
Does code already exist that recognises the programming language of a text file? (Surely this must be a less complicated task than eclipse's syntax trees or than google translate's language guessing feature, right?) In fact, does the SO syntax highlighter do anything like this?
Is it theoretically possible to create a single interpreter or compiler that recognises what language idiom you're using at any moment and (maybe "intelligently") executes or translates to a runnable form. And flags the corner cases where my syntax is ambiguous with regards to behaviour. Immediate difficulties I see include: knowing when to switch between indentation-dependent and brace-dependent modes, recognising funny operators (like *pointer vs *kwargs) and knowing when to use list vs array-like representations.
Is there any language or interpreter in existence, that can manage this kind of flexible interpreting?
Have I missed an obvious obstacle to this being possible?
edit
Thanks all for your answers and ideas. I am planning to write a constraint-based heuristic translator that could, potentially, "solve" code for the intended meaning and translate into real python code. It will notice keywords from many common languages, and will use syntactic clues to disambiguate the human's intentions - like spacing, brackets, optional helper words like let or then, context of how variables are previously used etc, plus knowledge of common conventions (like capital names, i for iteration, and some simplistic limited understanding of naming of variables/methods e.g containing the word get, asynchronous, count, last, previous, my etc). In real pseudocode, variable naming is as informative as the operations themselves!
Using these clues it will create assumptions as to the implementation of each operation (like 0/1 based indexing, when should exceptions be caught or ignored, what variables ought to be const/global/local, where to start and end execution, and what bits should be in separate threads, notice when numerical units match / need converting). Each assumption will have a given certainty - and the program will list the assumptions on each statement, as it coaxes what you write into something executable!
For each assumption, you can 'clarify' your code if you don't like the initial interpretation. The libraries issue is very interesting. My translator, like some IDE's, will read all definitions available from all modules, use some statistics about which classes/methods are used most frequently and in what contexts, and just guess! (adding a note to the program to say why it guessed as such...) I guess it should attempt to execute everything, and warn you about what it doesn't like. It should allow anything, but let you know what the several alternative interpretations are, if you're being ambiguous.
It will certainly be some time before it can manage such unusual examples like #Albin Sunnanbo's ImportantCustomer example. But I'll let you know how I get on!
I think that is quite useless for everything but toy examples and strict mathematical algorithms. For everything else the language is not just the language. There are lots of standard libraries and whole environments around the languages. I think I write almost as many lines of library calls as I write "actual code".
In C# you have .NET Framework, in C++ you have STL, in Java you have some Java libraries, etc.
The difference between those libraries are too big to be just syntactic nuances.
<subjective>
There has been attempts at unifying language constructs of different languages to a "unified syntax". That was called 4GL language and never really took of.
</subjective>
As a side note I have seen a code example about a page long that was valid as c#, Java and Java script code. That can serve as an example of where it is impossible to determine the actual language used.
Edit:
Besides, the whole purpose of pseudocode is that it does not need to compile in any way. The reason you write pseudocode is to create a "sketch", however sloppy you like.
foreach c in ImportantCustomers{== OrderValue >=$1M}
SendMailInviteToSpecialEvent(c)
Now tell me what language it is and write an interpreter for that.
To detect what programming language is used: Detecting programming language from a snippet
I think it should be possible. The approach in 1. could be leveraged to do this, I think. I would try to do it iteratively: detect the syntax used in the first line/clause of code, "compile" it to intermediate form based on that detection, along with any important syntax (e.g. begin/end wrappers). Then the next line/clause etc. Basically write a parser that attempts to recognize each "chunk". Ambiguity could be flagged by the same algorithm.
I doubt that this has been done ... seems like the cognitive load of learning to write e.g. python-compatible pseudocode would be much easier than trying to debug the cases where your interpreter fails.
a. I think the biggest problem is that most pseudocode is invalid in any language. For example, I might completely skip object initialization in a block of pseudocode because for a human reader it is almost always straightforward to infer. But for your case it might be completely invalid in the language syntax of choice, and it might be impossible to automatically determine e.g. the class of the object (it might not even exist). Etc.
b. I think the best you can hope for is an interpreter that "works" (subject to 4a) for your pseudocode only, no-one else's.
Note that I don't think that 4a,4b are necessarily obstacles to it being possible. I just think it won't be useful for any practical purpose.
Recognizing what language a program is in is really not that big a deal. Recognizing the language of a snippet is more difficult, and recognizing snippets that aren't clearly delimited (what do you do if four lines are Python and the next one is C or Java?) is going to be really difficult.
Assuming you got the lines assigned to the right language, doing any sort of compilation would require specialized compilers for all languages that would cooperate. This is a tremendous job in itself.
Moreover, when you write pseudo-code you aren't worrying about the syntax. (If you are, you're doing it wrong.) You'll wind up with code that simply can't be compiled because it's incomplete or even contradictory.
And, assuming you overcame all these obstacles, how certain would you be that the pseudo-code was being interpreted the way you were thinking?
What you would have would be a new computer language, that you would have to write correct programs in. It would be a sprawling and ambiguous language, very difficult to work with properly. It would require great care in its use. It would be almost exactly what you don't want in pseudo-code. The value of pseudo-code is that you can quickly sketch out your algorithms, without worrying about the details. That would be completely lost.
If you want an easy-to-write language, learn one. Python is a good choice. Use pseudo-code for sketching out how processing is supposed to occur, not as a compilable language.
An interesting approach would be a "type-as-you-go" pseudocode interpreter. That is, you would set the language to be used up front, and then it would attempt to convert the pseudo code to real code, in real time, as you typed. An interactive facility could be used to clarify ambiguous stuff and allow corrections. Part of the mechanism could be a library of code which the converter tried to match. Over time, it could learn and adapt its translation based on the habits of a particular user.
People who program all the time will probably prefer to just use the language in most cases. However, I could see the above being a great boon to learners, "non-programmer programmers" such as scientists, and for use in brainstorming sessions with programmers of various languages and skill levels.
-Neil
Programs interpreting human input need to be given the option of saying "I don't know." The language PL/I is a famous example of a system designed to find a reasonable interpretation of anything resembling a computer program that could cause havoc when it guessed wrong: see http://horningtales.blogspot.com/2006/10/my-first-pli-program.html
Note that in the later language C++, when it resolves possible ambiguities it limits the scope of the type coercions it tries, and that it will flag an error if there is not a unique best interpretation.
I have a feeling that the answer to 2. is NO. All I need to prove it false is a code snippet that can be interpreted in more than one way by a competent programmer.
Does code already exist that
recognises the programming language
of a text file?
Yes, the Unix file command.
(Surely this must be a less
complicated task than eclipse's syntax
trees or than google translate's
language guessing feature, right?) In
fact, does the SO syntax highlighter
do anything like this?
As far as I can tell, SO has a one-size-fits-all syntax highlighter that tries to combine the keywords and comment syntax of every major language. Sometimes it gets it wrong:
def median(seq):
"""Returns the median of a list."""
seq_sorted = sorted(seq)
if len(seq) & 1:
# For an odd-length list, return the middle item
return seq_sorted[len(seq) // 2]
else:
# For an even-length list, return the mean of the 2 middle items
return (seq_sorted[len(seq) // 2 - 1] + seq_sorted[len(seq) // 2]) / 2
Note that SO's highlighter assumes that // starts a C++-style comment, but in Python it's the integer division operator.
This is going to be a major problem if you try to combine multiple languages into one. What do you do if the same token has different meanings in different languages? Similar situations are:
Is ^ exponentiation like in BASIC, or bitwise XOR like in C?
Is || logical OR like in C, or string concatenation like in SQL?
What is 1 + "2"? Is the number converted to a string (giving "12"), or is the string converted to a number (giving 3)?
Is there any language or interpreter
in existence, that can manage this
kind of flexible interpreting?
On another forum, I heard a story of a compiler (IIRC, for FORTRAN) that would compile any program regardless of syntax errors. If you had the line
= Y + Z
The compiler would recognize that a variable was missing and automatically convert the statement to X = Y + Z, regardless of whether you had an X in your program or not.
This programmer had a convention of starting comment blocks with a line of hyphens, like this:
C ----------------------------------------
But one day, they forgot the leading C, and the compiler choked trying to add dozens of variables between what it thought was subtraction operators.
"Flexible parsing" is not always a good thing.
To create a "pseudocode interpreter," it might be necessary to design a programming language that allows user-defined extensions to its syntax. There already are several programming languages with this feature, such as Coq, Seed7, Agda, and Lever. A particularly interesting example is the Inform programming language, since its syntax is essentially "structured English."
The Coq programming language allows "syntax extensions", so the language can be extended to parse new operators:
Notation "A /\ B" := (and A B).
Similarly, the Seed7 programming language can be extended to parse "pseudocode" using "structured syntax definitions." The while loop in Seed7 is defined in this way:
syntax expr: .while.().do.().end.while is -> 25;
Alternatively, it might be possible to "train" a statistical machine translation system to translate pseudocode into a real programming language, though this would require a large corpus of parallel texts.
I love Ruby, for past couple of years it is my language of choice.
But even since I started learning it, I was repelled with the fact that so often there are several ways to do the same (or equivalent) thing. I'll give couple of examples:
methods often have aliases, so you always have to bother to choose the most adequate, popular or commonly accepted alternative
and and or, besides && and || - just look at how much confusion precedence difference among them causes
for keyword, used almost exclusively by inexperienced non-native Ruby developers
What was the rationale behind such design decisions? Did they (Matz?) believe that the language will be easier to adopt, and therefore more popular that way?
Ruby is inspired by Perl, and one important Perl philosophy is "There is more than one way to do it", i.e. redunancies are fine since they give the programmer more freedom (and increases the odds that the functionality they want is available under the name they'd give it - not only under one). Your decision whether that's actually a good thing.
When Matz wrote Ruby, he tried to follow the 'Principle of Least Surprise'. Often this meant that there'd be more than one way to do the same thing, for example assigning to arrays by using square brackets, or an insert method. I enjoy it, because I find that rather than trying to remember which exact name to use in which situation (I always used to pause for a moment for size vs length in Java), I just just write what seems logical, and usually it will work. When reading the code, it's normally not a problem to use a different name, as the names are usually self-explanatory. So, I don't worry about which is most adequate or popular, I choose the most logical at the time.
Matz was also inspired by Perl, which has 'There's more than one way to do it' as its slogan.
I don't believe Matz was worried about what would be most popular, he just wanted to write the language he wanted to use.
I'm not going to try to explain and vs && though...
Beware that and vs. &&, though similar, have different precedence.
a = b && c # => equivalent to a = (b and c). a is set to a boolean.
a = b and c # => equivalent to (a = b) and c. a is set to b, and expression is a boolean.
There's more than one way to do it, but there may be subtle differences between them.
(update, just noticed you mentioned the precedence difference in your question... sorry. nothing to see here. move along.)
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Closed 9 years ago.
I heard people say they can understand their python code a year later but not their XYZ code. Why? I dont know what is good about python syntax or what is bad about another. I like C# but i have a feeling VB.NET code is easier to read. I am doing language design so what do you find makes code/syntax/language readable or not readable?
Experience.
IMO, one of the big things is significant white space. Block indention goes a long ways and languages like Python and F# that provide a level of significant white space can help with readability.
Code like Java and C# tend to be structured and the readability becomes a focal point of how it was coded to begin with and not of the language itself.
Code is readable when its written in a style of explicit "stating what you want to do".
This only depends on the language in sofar
it allows you to express what you want (functional-programming!)
it doesn't emphasize on cryptical statements
The rest depends on the style you use to write code (even Perl can be understandable!), but certain languages make it easier to hacky statements.
Clear:
expr = if not (ConditionA and ConditionB) then ... else ...
Unclear:
expr = (!(conditionA && conditionB)) ? ... : ...
Clear:
foreach line in lines:
if (line =~ /regex/):
// code
Unclear:
... if /regex/ foreach(#lines);
Clear:
x = length [ x | x <- [1..10], even x ]
Unclear:
int x = 0;
for (int i = 1; i <= 10; ++i)
if ((i&&1)==0) ++x;
Generally what makes Python considered readable is that it forces a standardized indentation. This means that you'll never be forced to wonder whether you're in an if block or a function, it is clear as day. Even poorly written code therefore becomes obvious.
One language which I generally consider difficult to read is PHP for the same reason (or rather, its opposite). Since programmers are allowed to indent at will, and store variables anywhere, it can get convoluted very quickly. Further, since PHP historically did not have case sensitive function names (PHP < 4.4.7 I believe), this means that there really isn't a consistency in the implementation of the core language either... (Don't get me wrong, I like the language, but a bad coder can REALLY make a mess).
JavaScript also has a lot of problems with undisciplined developers. You'll find yourself wondering where variables have been defined and what scope you're in. Code will not be in one consolidated place, but rather spread across multiple files, and often lurking where unexpected.
ActionScript 3 is a bit better. Generally, there has been a move to have everyone use similar syntax's, and Adobe has gone so far as to define its standards and make them accessible and common. It does not take much to see how the ECMAScript implementation which is supported by a for-profit company is superior to the generalized one.
Readability is a function that takes a lot of inputs. I don't think it's really possible to compile a full list of things that can affect a language's readability. The most general way to describe it is "minimizing cognitive load." A few major factors:
Subtleties of meaning. If two code snippets look very similar at a glance but do different things, it hurts readability because the reader has to stop and deduce what's actually happening.
Meaningless code — aka boilerplate. This doesn't necessarily mean code that does nothing, but code that doesn't tell me anything about what we're actually doing. Every bit of code that doesn't express the actual intent of a function or object reduces readability by that much.
Cramming meaning — aka golf. This is the opposite of the boilerplate problem. It's possible to compress code so far that the reader is forced to stop and examine it pretty much character by character. The exact line where this occurs is somewhat subjective (which is part of why some people love Perl and some people hate it), but it's definitely a real phenomenon.
The programmer makes code readable or unreadable, not the language. Thinking otherwise is just fooling yourself. This is because the only people who are qualified to judge readability are those who know the language. To the non-programmer, all languages are equally unreadable.
I heard people say they can understand their python code a year later but not their XYZ code. Why?
Firstly, I don't think that people say that based solely on syntax. There are a lot of other factors to take into consideration, to name just a few:
The fact that some languages tend to promote only one right way to do something (like Python), and others promote many different ways (Ruby for example, from what I hear [disclaimer: I am not a Ruby programmer])
The libraries the language has. The better designed ones tend to be incredibly easy to understand without needing documentation, and this also tends to help remember. A language with good libraries will therefore make things easier.
Having said that, my personal take on Python is the fact that many people call it "executable pseud-code". It supports a wide variety of things that tend to appear in pseudo-code, and as an extension, are the standard way to think about things.
Also, Python's un-C-like syntax, one of the features that make it so disliked by so many people, also makes Python look more like pseudocode.
Well, that's my take on Python's readability.
To be honest when it comes to what makes a language readable it is really seems to boil down to a combination of simplicity and personal preference. (Of course - it is always possible to write unreadable code in any language if you try hard enough). Since personal preference can't really be controlled, it comes down to ease of expression - the more complicated it is in a language to use simple features, the more difficult that language is likely to be in general from a readability standpoint.
A word required when one character will suffice - a stone in the garden of Pascal and VB.
Compare:
Block ()
Begin
// Content
End
vs.
Block
{
// Content
}
It requires extra brain processing to read a word and mentally associate it with a concept, while a single symbol is immediately recognized by its image.
It is the same thing as the difference with natural languages, usual textual languages vs. symbol languages with hieroglyphs (Asian group). The processing of the first group is slower because basically a text is parsed to a set of concepts while hieroglyphs represent concepts themselves. Compare it with what you already know - will a serialization/deserialization from an XML be faster than a custom search over a binary format?
IMHO, the more a computer language resembles a spoken language, the more readable it is. For extreme examples, take languages like J or Whitespace or Brainfuck... completely unreadable to the untrained eye.
But a language that resembles English can be more easily understood. Not that this makes it the best language, as COBOL can attest.
I think it has more to do with the person writing the code rather than the actual language itself. You can write very readable code in any language, and unreadable code in any language. Even a complex Regular expression can be formatted and commented so as to make it easy to read.
a coworker of mine use to have a saying: "You can write crap code in any language." I liked it and wanted to share today. What makes code readable? Here are my thoughts
The ability to read the syntax of the language.
Well formatted code.
Meaningfully named variables and functions
Comments to explain complex processing. Beware, too much commentes can make the code hard to read
Short functions are easier to read than long ones.
None of these have anything to do with the language, it's all about the coder, and the quality of their work.
I will try saying that a code is readable by its simplicity.
You got to get at first sight what it does and what its purpose is. Why write a thousand lines of code when only a few does what is required?
This is the spirit of a functional language like F#, for instance.
For me its mainly the question of wether the language allows you to develop more readable abstractions which do prevent getting lost in details.
This is where OOP comes in very handy with the hiding of details. If i can hide the details of a task behind an interface that has the behavior of a common concept (i.e. iterators in C++) i usually don't have to read the implementation details.
I think, language design (for normal languages, not brainfuck :) ) not matters. To make code readable you should follow standards, code conventions, and don't forget about refactoring.
It's all about clean code.
Keep it small, simple, well named, and formatted.
class ShoppingCart {
def add(item) {
println "you added some $item"
}
def remove(item) {
println "you just took out the $item"
}
}
def myCart = new ShoppingCart()
myCart.with {
add "juice"
add "milk"
add "cookies"
add "eggs"
remove "cookies"
}
The literacy level of the reader.
Two distinct aspects, really. First is syntax and whitespace. Python enforces a whitespace standard, dropping unnecessary {, } and ; characters. This makes it easy on the eyes. Second, and most importantly, clarity of expression- i.e. how easy is it to map code back to the way you think. There are several features (and non-features) in programming languages that contribute to the latter point:
Disallowing jumps. The goto statement in C is a typical example. Code that doesn't keep running out of structured blocks is easier to read.
Minimizing side-effects. Global variables are evil, remember?
Using more tailored functions. How can your head track a for loop with 5 iteration variables? The Common Lisp loop is much easier to read (although VERY difficult to write, but that's a different story)
Lexical closures. You can figure out a variable's value by just looking at it, as opposed to running the code in your head, and then figuring out which statement is shadowing which.
A couple of examples:
(loop
do for tweet = (master-response-parser (twitter-show-status tweet-id))
for tweet-id = tweet-id then (gethash in-reply-to tweet)
while tweet-id
collecting tweet)
and
listOfFacs = [x | x <- [1 ..], x == sumOfFacDigits x]
where sumOfFacDigits x = sum [factorial (x `div` y) | y <- [1 .. 10]]
Concerning the syntax, I think it it imperative that it be fairly descriptive. For instance, in many languages, you have the foreach statement, and each one handles it a bit differently.
// PHP
foreach ($array as $variable) ...
// Ruby
array.each{ |variable| ... }
// Python
for variable in array ...
// Java
for (String variable : array)
Honestly, I feel that PHP and Python have the clearest means of understanding, but, it all boils down to how smart and clear the programmer wants to be. For instance, a bad programmer could write the following:
// PHP
foreach ($user as $_user) ...
My guess is that you would have almost no idea what the heck the code is doing unless you tracked back and attempted to figure out what $user was and why you were iterating over it. Being clear and concise is all about making small chunks of code make sense without having to trace back through the program to figure out what variables/function names are.
Also, I would have to completely agree with whitespace. Tabs, newlines and spacing in-between operators really make a huge difference!
Edit 1: I might also interject that some languages have the syntax and tools readily available to make things more clear. Take Ruby for example:
if [1,2,3].include? variable then ... end
verses, say Java:
if (variable != 1 || variable != 2 || variable != 3) { ... }
One of these (IMHO) is certainly more clear and readable than the other.