I know there is a notation or convention that for example describes the usage of a command (in a shell for example).
/<command> [arg0|arg1]
means the following is a right way of expressing/using the command: /TheNameOfTheCommand arg0 or /TheNameOfTheCommand arg1.
It is a bit like RegEx or a formal language. Minecraft uses this notation too to describe the syntax of their command. And I once heard about it by a professor in a programming lecture. That's the reason I think it must be a real convention.
Do you know the name of this convention or does it exist at all?
It's a convention, but not a standard. Or maybe it would be more accurate to say that it is a convention adapted from a collection of standards which differ in details, except that the standards derive from the conventional use, and it's more common to find other variants than strict application of the standards.
The use of angle brackets to delimit grammatical variables goes back to Peter Backus' notation to describe the original Algol (1959); the use of brackets to donate optionality and vertical bars to list alternatives was used in the definition of Pascal (1974) and promoted by Niklaus Wirth in a note published in 1977 (“What Can We Do About the
Unnecessary Diversity of Notation for
Syntactic Definitions”).
In the Pascal report, it was called "Extended Backus Naur Form", and it is one of a number of similar notations which go by that name. I think that's unfortunate because it doesn't acknowledge Wirth's contribution but if you called it WBNF people would probably think you were talking about a radio station.
(Wirth didn't always use angle brackets. In the published version of the Pascal report, grammatical variables were printed on italics, but in the widely-distributed typed manuscript, angle brackets were used. Similarly, literal tokens were sometimes typeset in boldface and sometimes typed surrounded by quotation marks.)
Related
Our application relies on lots of equations, which, to correspond with the standard scientific names, use variable names like mu_k, (if the standard is $\mu_k$). (We could debate whether scientists should switch to CS style descriptive variable names, but often the terms don't really describe anything, they are just part of equations, and, more over, we need our code to match the known literature.)
In C this is easy to name vars this way: int mu_k. We are considering porting our code to Scala, but I know that val mu_k is discouraged in Scala, because underscores have special meanings.
If we use underscores only in the middle of the var name (e.g. mu_k) and not beginning or end (e.g. _x or x_), will this present a problem in Scala?
What is the recommended naming convention for Scala in this case?
You are right that underscores are discouraged in variable names in Scala, which implies that they are not forbidden. In my opinion, a convention should be followed wherever sensible.
In the case of mathematical formulae, I disagree that the Greek letters don't convey a meaning; the meaning is not necessarily intuitively descriptive for non-mathematicians, but as you say, the reference to the usage in a paper may be meaningful and important. Therefore, sticking with the underscore won't hurt, although I would probably prefer a more Scala-style way as muX when possible and meaningful. If you want a perfect answer, you might need to perform a usability test with your developers. In the specific example, I personally find mu_x more readable than muX, but that might differ among individuals.
I don't think the Scala compiler has a problem with underscores in the examples you described. Presumably, even leading and trailing underscores are fine, but should indeed be avoided strictly because they have a special meaning: http://docs.scala-lang.org/style/naming-conventions.html#methods.
Underscores are not special in any way in identifiers. There are a lot of special meanings for the underscore in Scala, but not in identifiers. (There is a special rule in identifiers that if you want to mix alphanumeric characters and operator characters in the same identifier, they have to be separated by an underscore, e.g. foo? is not a legal identifier, but foo_? is.)
So, there is no problem using an identifier with an underscore in it.
It is generally preferred to use camelCase and PascalCase for alphanumeric identifiers, and not mix alphanumeric and operator characters in the same identifier (i.e. use maxBy instead of max_by and use isFoo instead of foo_?) but that's just a coding convention whose purpose is to reduce the number of "unspecial" underscores, so that you can quickly scan for the "special" ones.
But in your case, you are using special naming conventions anyway, so you don't need to adhere to the community naming conventions as strictly.
However, I personally would actually prefer the name µ_k over mu_k.
That's as far as it goes with Scala, unfortunately. The Fortress programming language by Sun/Oracle did allow boldface, overstrike, superscripts and subscripts in identifier names, so something like µk would have been possible as a legal identifier, but sadly, Fortress was abandoned a couple of years ago.
I'm not stating this is the correct way, and myself would be rather discouraged to do this, but you can use full string literals as identifiers:
From: http://www.scala-lang.org/files/archive/spec/2.11/01-lexical-syntax.html
id ::= plainid
| ‘’ stringLiteral ‘’
Finally, an identifier may also be formed by an arbitrary string
between back-quotes (host systems may impose some restrictions on
which strings are legal for identifiers). The identifier then is
composed of all characters excluding the backquotes themselves.
So this is valid:
val ’mu k‘
(sorry, for formatting)
I wish to code fully with Esperanto lexemes. That is, not ending up with a English/Esperanto mix up. Perligata is a good example of the kind of result I would like, but it use Latin where I want to use Esperanto.
So Perl seems to be a valid answer to my question. On the other end a language like Python have no mechanism that would let you use se (if in esperanto) rather than if. On what you may call middle ground, you have languages like C that allow to replace keywords through its processor (#define se if), but won't allow you to get ride of the define keywords itself. Also you have languages like racket and the LISP-family that would probably let you use wrap most internal symbols, but probably not allow you to easily change parentheses for anything else. For example mapping ( with ene and ) with ele.
Also an other point is ability to use unicode in identifiers, as Esperanto do use non-ASCII characters in its alphabet, like ĉ. That's not really a blocking element, as one is available to use cx instead of ĉ, but its nevertheless an interesting parameter.
So I guess an ideal answer to this question would be a matrix of languages specifying their lexeme and grammar customability.
each formal language has its syntax. in my opinion, lowest 'syntax overhead' is offered by lisp-like languages. but then you don't want to have parenthesis. you also don't want to have #define therefore you reject any syntax at all and all possible replacements.
i don't think there is any language that will let you do it. you should look for language generators, write your own language (at least the syntax part) or the simplest possible way, add your own find-replace layer on top of any existing language
I have read some articles online on the naming convention for Perl style which suggest using lowercase letters and separating words by underscore for functions or methods names. Some others use the first word in lowercase then capitalize the other words. Of course Windows .NET etc Capitalize every word and no underscore.
I have some packages methods many words like entriesoncurrentpage, if I follow Perl style suggested I should do it like:
sub entries_on_current_page {...}
this added four underscore letters to the method name, the other style is:
sub entriesOnCurrentPage {...}
and Windows style should be:
sub EntriesOnCurrentPage {...}
PHP sometimes uses all lowercase with underscore like mysql_real_escape_string() and sometimes uses all lowercase without underscore like htmlspecialchars, of course PHP function names are not case sensitive so this feature is not supported in Perl.
So the question is, for the long name with many words what is the best style to use for Perl coding.
Originally, most Perl developers used camel casing with the first letter lowercased. This is the standard with most programming languages. Names with first letter capitalized were used for classes and methods.
Later on, Damian Conway's book Perl Best Practices suggested using underscores rather than camel casing. Damian argued that it increased readability, and was not that much harder to type.
Damian Conway's suggestion on names became the standard because 1). He was correct. It's much more legible and isn't that much harder to type, and most importantly 2). It was incorporated into Perltidy. Perltidy is a program that helps standardize your code according to Damian's suggestions. Perltidy is much like CheckStyle in Java.
Are these arbitrary standards? Yes, all standards are somewhat arbitrary in nature. You have a few candidate suggestions for rules, and you must make a decision:
Should the curly brace in while loops and if statements be appended on the end of the line, or go under the while or if statement. In standerd C style, curly braces are cuddled. In Java, they're not suppose to be according to CheckStyle. In Kornshell, the then goes under the if. In Bash, the standard is now that the then goes on the same line even though the Bash interpreter doesn't really like it. (You have to add a semicolon before the then because it's considered a separate command.
How should variable names be done. In most languages, CamelCase rules. In .NET, you even capitalize the first character, but in Perl, we use underscores.
Should constants be all uppercase? Most languages have agreed with that. However, in shell script, you usually reserve all uppercase variable names for special environment variables such as $PWD, $PATH, etc. Therefore, in Bash and Kornshell scripts, constant variables are all camelCased like regular variables.
The idea is to follow the standard for that language. Why? Because the standard says so. Because you can't argue with The Standard as you can with your fellow programmers whether or not curly braces are cuddled or not. The main this is to realize that most standards may be somewhat arbitrary, but they don't really affect the way you program. By everyone following a standard, you make it easier to understand other people's code.
What's the reason of this recommendation? Why not keeping consistent with other programming languages which use underscore instead?
I think that LISP uses the hyphen for two reasons: "history" and "because you can".
History
LISP is an old language, and in the early days typing an underscore could be challenging. For example, the first terminal I used for LISP was an ASR-33 teletype. On some hosts and teletype models, the key sequence for the underscore character would be interpreted as a left-pointing arrow (the assignment operator in Smalltalk). Hyphens could be typed more reliably.
Because You Can
In LISP, there are no infix operators (well, few). So there is no ambiguity concerning whether x-1 means "x minus 1" or "x hyphen 1". The early pioneers liked the look of the hypen for multiword symbols (or were stuck on ASR-33s as well :).
Just a guess: it may be because it resembles English language's compound words (like "well-known", "merry-go-round", etc). Like Paul said in comment, it's one of the oldest languages and for the creators of LISP hyphen might have seemed more natural than, for example, an underscore.
Side note: I, personally, do like it, because it separates words, but at the same time makes the long identifier look as a whole (compare fooBarBaz, foo-bar-baz and foo_bar_baz).
In written natural languages the - sign is often used as a way to make compound words. In German for example we compose german nouns just by appending them:
Hofbräuhaus
Above consist of three parts: Hof bräu haus.
But when we write concepts in German which have foreign names as their part we write them like this:
Mubarak-Regime
In natural languages it is not common to compose words by CamelCase or Under_Score.
The design of most Lisps was more oriented towards the linguistic tradition. The convention in some languages to use the underscore came up, because in these languages the - sign was already taken for the minus operation and the identifiers of theses were not allowed to include the - sign. The - sign is a identifier terminating character in these languages. Not in Lisp.
Note though that one can use the underscore in Lisp identifiers, though this is rarely use in code for aesthetic reasons.
One can also use every character in an identifier. The vertical bar encloses an arbitrary symbol:
|this *#^! symbol is valid - why is that po_ss_ib_le?|
> (defun |this *#^! symbol is valid - why is that po_ss_ib_le?| (|what? really?|)
(+ |what? really?| 42))
|this *#^! symbol is valid - why is that po_ss_ib_le?|
> (|this *#^! symbol is valid - why is that po_ss_ib_le?| 42)
84
Note that the backslash is an escape character in symbol names.
I'm sure I join many in being glad there's finally a powerful language tied tightly to a mainstream GUI/Database/Communication framework.
I haven't been sure where to post this, but here seems the best spot.
I need to use Unicode symbol characters either as operators or as function names. I'd like syntactic sugar, but I don't need it.
Guy Steele pointed out in Communications of the ACM that "*" was a forced choice when it was adopted from Ascii as multiply, but my software works in Unicode, so I'm not tethered to Ascii anymore.
!$%&*+-./<=>?,#^|~:
Part of localization includes local programmers. Why limit the set of operators that can be defined in F#? It isn’t orthogonal to C#'s and F#'s acceptance of many Unicode IsLetter in identifiers.
Also, F# is likely to be used for symbolic manipulation of problems from logic, math, physicists, etc. It makes work much easier if there’s a direct mapping into the language of the basic operators. (F# and C# accept many Unicode IsLetter? as well as IsDigit’? This is a request to allow Unicode IsSymbol? As operators with the precedence of, for example, *, or, since “+” is both a unary and binary operator, I could put up with the precedence of + and make up the difference with parenthesized groupings.
Consider the domain-specific needs of logicians, mathematicians, physicists, etc. I’d rather write a symbolic differentiator or integrator using math symbols than Ascii permutations of already-taken operators.
Logic: ∀ ∃ ⇒
Math: ∑ ∫ ∂
Group theory: ≤ ≥ ∈ ∉
Set Theory: ⊆ ⊇ ⊃ ∪ ∩
Tensors: ⊗
I’ve written many languages in other languages, but because F# is tightly .Net-integrated, this issue poses special challenges without language support:
It’s trivial to cobble up a translator that takes Unicode-operator F# source and maps it, line-by-line, to Ascii-operator F# source.
But when debugging, how do I make sure the programmer still sees their untranslated source? And that they can see variable values.
Operators and converts them is trivial. But how do I ensure the translation is what gets compiled, while the programmer sees their own source? If I map line-for-line correctly, how do I ensure they can still point at a variable and see its value?
There is a math (Unicode) symbol extension for F# available in the Visual Studio Gallery.
This allows you to define Unicode symbols, e.g.:
let inline (~∑) xs = xs |> Seq.sum
let total = ∑myList
You may be interested in Project Fortress which is a new functional programming language that embraces the Unicode character set (among many other features). In particular, see the Mathematical Syntax in Fortress page which contains some sample code.
For an interesting discussion on this check: http://cs.hubfs.net/forums/thread/9690.aspx
Other languages, such as Scala, do permit operators from outside the ASCII range -- mathematical symbols(Sm) and other symbols(So)