From da673e6f329fd73c698eba2b8b0cf9851b441792 Mon Sep 17 00:00:00 2001 From: "Achim D. Brucker" Date: Thu, 9 Aug 2018 21:42:58 +0100 Subject: [PATCH] Improved Markdown. --- CodingStyle.md | 102 ++++++++++++++++++++++++++++++++++++------------- 1 file changed, 75 insertions(+), 27 deletions(-) diff --git a/CodingStyle.md b/CodingStyle.md index 0154cdf..747af10 100644 --- a/CodingStyle.md +++ b/CodingStyle.md @@ -1,4 +1,5 @@ # su4sml coding style + We here document coding-style guidelines that should be adhered to. Much of the existing code is not yet following these guidelines, patches are welcome. This style-guide was inspired by the SML Style @@ -7,6 +8,7 @@ Guide from ## Chapter 1: Indentation and breaking long lines + The limit on the length of lines is 80 columns and this is a hard limit. Using more than 80 columns causes your code to wrap around to the next line, which is devastating to readability. @@ -16,6 +18,7 @@ spaces to control indenting. Indent by two spaces. Long expressions can be broken up and the parts aligned, as in the second example. Either is acceptable. + ```sml val x = "Long line..."^ "Another long line." @@ -23,13 +26,17 @@ val x = "Long line..."^ val x = "Long line..."^ "Another long line." ``` + Case expressions should be indented as follows: + ```sml case expr of pat1 => ... | pat2 => ... ``` + If expressions should be indented according to one of the following schemes: + ```sml if exp1 then exp2 if exp1 then else if exp3 then exp4 exp2 @@ -39,6 +46,7 @@ else if exp5 then exp6 else exp3 if exp1 then exp2 else exp3 if exp1 then exp2 else exp3 ``` + Comments should be indented to the level of the line of code that follows the comment. @@ -55,6 +63,7 @@ multiple lines to something that has good style is to factor the code using a let expression. Consider the following: * Bad + ```sml fun euclid (m:int,n:int) : (int * int * int) = if n=0 @@ -65,6 +74,7 @@ let expression. Consider the following: ``` * Better + ```sml fun euclid (m:int,n:int) : (int * int * int) = if n=0 @@ -75,7 +85,9 @@ let expression. Consider the following: #3 (euclid (n, m mod n))) ``` + * Best + ``` fun euclid (m:int,n:int) : (int * int * int) = if n=0 @@ -90,7 +102,9 @@ let expression. Consider the following: ``` Do not factor unnecessarily. + * Bad + ```sml let val x = TextIO.inputLine TextIO.stdIn @@ -101,25 +115,31 @@ Do not factor unnecessarily. ``` * Good + ```sml case TextIO.inputLine TextIO.stdIn of ... ``` -* Bad (provided y is not a large expression): + +* Bad (provided `y` is not a large expression): + ```sml let val x = y*y in x+z end ``` * Good + ```sml y*y + z ``` ## Chapter 3: Comments + Comments should be written with [SMLDoc](http://www.pllab.riec.tohoku.ac.jp/smlsharp/?SMLDoc) in mind; a, nightly updated, API documentation is [available](http://projects.brucker.ch/su4sml/smldoc/). For example: + ```sml (** * opens a file. @@ -129,7 +149,9 @@ a, nightly updated, API documentation is * @return file stream *) val openFile : {fileName : string, mode : openMode} -> stream ``` + We mainly restrict ourselves to the following SMLDoc tags: + ``` @params gives names to formal parameters of functions and value constructors @param a description of a formal parameter @@ -137,18 +159,21 @@ We mainly restrict ourselves to the following SMLDoc tags: @see related items (specified text is not analyzed in the current version) @throws same as the @exception tag ``` + Signatures must be commented using SMLDoc. Comments go above the code they reference, as in the following example: + ```sml (** Sums a list of integers. *) val sum = foldl (op +) 0 ``` -Avoid Useless Comments. Avoid comments that merely repeat the code they + +*Avoid Useless Comments.* Avoid comments that merely repeat the code they reference or state the obvious. Comments should state the invariants, the non-obvious, or any references that have more information about the code. -Avoid Over-commenting. Very many or very long comments in the code body are +*Avoid Over-commenting.* Very many or very long comments in the code body are more distracting than helpful. Long comments may appear at the top of a file if you wish to explain the overall design of the code or refer to any sources that have more information about the algorithms or data structures. All other @@ -156,7 +181,7 @@ comments in the file should be as short as possible. A good place for a comment is just before a function declaration. Judicious choice of variable names can help minimize the need for comments. -Line Breaks. Empty lines should only be included between value declarations +*Line Breaks.* Empty lines should only be included between value declarations within a struct block, especially between function declarations. It is not necessary to put empty lines between other declarations unless you are separating the different types of declarations (such as structures, types, @@ -164,10 +189,11 @@ exceptions and values). Unless function declarations within a let block are long, there should be no empty lines within a let block. There should never be an empty line within an expression. -Multi-line Commenting. When comments are printed on paper, the reader lacks the +*Multi-line Commenting.* When comments are printed on paper, the reader lacks the advantage of color highlighting performed by an editor such as Emacs. Multiline comments can be distinguished from code by preceding each line of the comment with a * similar to the following: + ```sml (** * This is one of those rare but long comments @@ -179,20 +205,21 @@ fun complicatedFunction () = ... ## Chapter 4: Parentheses -Over Parenthesizing. Parentheses have many semantic purposes in ML, including +*Over Parenthesizing.* Parentheses have many semantic purposes in ML, including constructing tuples, grouping sequences of side-effect expressions, forcing a non-default parse of an expression, and grouping structures for functor arguments. Their usage is very different from C or Java. Avoid using unnecessary parantheses when their presence makes your code harder to understand. -Case expressions. Wrap case expressions with parentheses. This avoids a +*Case expressions.* Wrap case expressions with parentheses. This avoids a common error involving nested case expressions. If the case expression is already wrapped by a let...in...end block, you can drop the parentheses. -Alternative Block Styles. Blocks of code such as let...in...end, struct...end, +*Alternative Block Styles.* Blocks of code such as let...in...end, struct...end, and sig...end should be indented as follows. There are several alternative styles to choose from. + ```sml fun foo bar = fun foo bar = fun foo bar = let let let val p = 4 val p = 4 @@ -203,16 +230,16 @@ fun foo bar = fun foo bar = fun foo bar = let end ``` - ## Chapter 5: Pattern matching -No Incomplete Pattern Matches. Incomplete pattern matches are flagged with +*No Incomplete Pattern Matches.* Incomplete pattern matches are flagged with compiler warnings, which should be treated as errors. -Pattern Match in the Function Arguments When Possible. Tuples, records and +*Pattern Match in the Function Arguments When Possible.* Tuples, records and datatypes can be deconstructed using pattern matching. If you simply deconstruct the function argument before you do anything useful, it is better to pattern match in the function argument. Consider these examples: + ```sml Bad Good fun f arg1 arg2 = let fun f (x,y) (z,_) = ... @@ -233,8 +260,7 @@ in end ``` - -Avoid Unnecessary Projections. Prefer pattern matching to projections with +*Avoid Unnecessary Projections.* Prefer pattern matching to projections with function arguments or a value declarations. Using projections is okay as long as it is infrequent and the meaning is clearly understood from the context. The above rule shows how to pattern-match in the function arguments. Here is @@ -251,12 +277,12 @@ in end end ``` - -Combine nested case Expressions. Rather than nest case expressions, you can +*Combine nested case Expressions.* Rather than nest case expressions, you can combine them by pattern matching against a tuple, provided the tests in the case expressions are independent. Here is an example: * Bad + ```sml let val d = Date.fromTimeLocal(Time.now()) @@ -275,6 +301,7 @@ case expressions are independent. Here is an example: ``` * Good + ```sml let val d = Date.fromTimeLocal(Time.now()) @@ -294,9 +321,9 @@ these functions altogether. It is usually easy to achieve the same effect with pattern matching. If you cannot manage to avoid them, you should handle any exceptions that they might raise. - ## Chapter 6: Naming and declarations -Naming Conventions. The best way to tell at a glance something about the type + +*Naming Conventions.* The best way to tell at a glance something about the type of a variable is to use the standard SML naming conventions. The following are the preferred rules that are (more or less) followed by the SML basis and SML/NJ libraries: @@ -322,11 +349,12 @@ These conventions are not enforced by the compiler, though violations of the variable/constructor conventions ought to cause warning messages because of the danger of a constructor turning into a variable when it is misspelled. -Use Meaningful Names. Another way of conveying information is to use meaningful +*Use Meaningful Names.* Another way of conveying information is to use meaningful variable names that reflect their intended use. Choose words or combinations of words describing the value. Variable names may be one letter in short let blocks. Functions used in a fold, filter, or map are often bound to the name f. Here is an example for short variable names: + ```sml let val d = Date.fromTimeLocal(Time.now()) @@ -338,7 +366,7 @@ in end ``` -Avoid Global Mutable Variables. Mutable values should be local to closures and +*Avoid Global Mutable Variables.* Mutable values should be local to closures and almost never declared as a structure's value. Global mutable values cause many problems. First, it is difficult to ensure that the mutable value is in the proper state, since it might have been modified outside the function or by a @@ -348,7 +376,7 @@ makes it more likely that your code is nonreentrant. Without proper knowledge of the ramifications, declaring global mutable values can extend beyond bad style to incorrect code. -When to Rename Variables. You should rarely need to rename values, in fact this +*When to Rename Variables.* You should rarely need to rename values, in fact this is a sure way to obfuscate code. Renaming a value should be backed up with a very good reason. One instance where renaming a variable is common and encouraged is when aliasing structures. In these cases, other structures used @@ -356,6 +384,7 @@ by functions within the current structure are aliased to one or two letter variables at the top of the struct block. This serves two purposes: it shortens the name of the structure and it documents the structures you use. Here is an example: + ```sml struct structure H = HashTable @@ -364,10 +393,12 @@ struct ... end ``` -Order of Declarations in a Structure. When declaring elements in a structure, + +*Order of Declarations in a Structure.* When declaring elements in a structure, you should first alias the structures you intend to use, followed by the types, followed by exceptions, and lastly list all the value declarations for the structure. Here is an example: + ```sml struct structure L = List @@ -383,16 +414,18 @@ Moreover, every top-level structure should be restricted by a (documented) signature. Functions should declared in their their curried form, e.g., + ```sml fun f x y = ... instead of fun f(x,y) = ... ``` + Datatypes should be preferred to type synonyms in particular for record types ## Chapter 7: Verbosity -Don't Rewrite Library Functions. The basis library and the SML/NJ library have +*Don't Rewrite Library Functions.* The basis library and the SML/NJ library have a great number of functions and data structures -- use them! Often students will recode List.filter, List.map, and similar functions. A more subtle situation for recoding is all the fold functions. Writing a function that @@ -400,7 +433,7 @@ recursively walks down the list should make vigorous use of List.foldl or List.foldr. Other data structures often have a folding function; use them whenever they are available. -Misusing if Expressions. Remember that the type of the condition in an if +*Misusing if Expressions.* Remember that the type of the condition in an if expression is bool. In general, the type of an if expression is 'a, but in the case that the type is bool, you should not be using if at all. Consider the following: @@ -418,9 +451,10 @@ if x then false else y not x andalso y if x then y else true not x orelse y ``` -Misusing case Expressions. The case expression is misused in two common +*Misusing case Expressions.* The case expression is misused in two common situations. First, case should never be used in place of an if expression (that's why if exists). Note the following: + ```sml case e of true => x @@ -428,8 +462,10 @@ case e of if e then x else y ``` + The latter is much better. Another situation where if expressions are preferred over case expressions is as follows: + ```sml case e of c => x (* c is a constant value *) @@ -437,13 +473,16 @@ case e of if e=c then x else y ``` + The latter is definitely better. The other misuse is using case when pattern matching with a val declaration is enough. Consider the following: + ```sml val x = case expr of (y,z) => y val (x,_) = expr ``` + The latter is better. Other Common Misuses. Here are some other common mistakes to watch out for: @@ -470,25 +509,30 @@ Int.sign(x)=1 x>0 Do not re-wrap Functions. When passing a function as an argument to another function, don't re-wrap the function unnecessarily. Here's an example: + ```sml List.map (fn x => Math.sqrt x) [1.0, 4.0, 9.0, 16.0] List.map Math.sqrt [1.0, 4.0, 9.0, 16.0] ``` + The latter is better. Another case for rewrapping a function is often associated with infix binary operators. To prevent rewrapping the binary operator, use the op keyword as in the following example: + ```sml foldl (fn (x,y) => x + y) 0 foldl (op +) 0 ``` + The latter is better. Don't Needlessly Nest let Expressions. Multiple declarations may occur in the first block of a let...in...end expression. The bindings are performed sequentially, so you may use a name bound earlier in the same block. Consider the following: + ```sml let val x = 42 @@ -521,12 +565,14 @@ with a name. In general, a source file should only contain one signature or structure. In more detail: -- if a signature is only implemented by one structure, the signature and + +* if a signature is only implemented by one structure, the signature and structure can be placed in one file, -- if a signature is implemented by several structures, the signature should +* if a signature is implemented by several structures, the signature should be placed into a separate file. + The file name should reflect the signature name and it should be -and separated by underscore, e.g., ocl_term.sig +and separated by underscore, e.g., `ocl_term.sig`. Source files should use the Unix line ending convention and be either encoding using ASCII (preferred) or UTF-8. @@ -541,7 +587,9 @@ of the SML standard library. ## Appendix + ### Appendix I: Machine-support + The following elisp-snippet provides marginal support for this coding-style for the [sml-mode](http://www.smlnj.org/doc/Emacs/sml-mode.html) of [Emacs](http://www.gnu.org/software/emacs/).