On 11 Feb 2002, Pixel wrote:

http://merd.net/pixel/language-study/syntax-across-languages.html

CHANGES: - the page has now much more entries - one can check the missing entries per language at http://merd.net/pixel/language-study/syntax-across-languages-per-language.ht... (160KB) see especially the haskell one http://merd.net/pixel/language-study/syntax-across-languages-per-language.ht...

Contributions, suggestions and fixes are welcome.

Some random thoughts.... Under * Object Oriented & Reflexivity +---------------------------------------+ | class | class declaration | |-------------------+-------------------| | functional syntax | method invocation | +---------------------------------------+ I'm not sure anything under haskell can be considered OO but I'm no languages expert. You might could mention something about Type classes. This is the main (only) method of overloading functions in haskell. maybe you might make mention of polymorphic type system and how haskell uses type inferencing to determine the meaning of expressions (relates to type classes). Using data = Foo ... really should be meantioned as a way to construct new types. newtype = Foo ... (new type) type Foo = ... is only a type synonym. heres an example. type String = [Char] Under constrol structure, at least give mention to monads! Common examples (ST,IO,List,Maybe) and "do notation" Monads are defined by instanciating them under the Monad type class. (basically giving definitions for the operators >>= (aka 'bind') and >> I dont think you give list comprehensions a fair shake either. (btw, list comprehension is an example of an alternative syntax for using lists as a monad.) [f z elem | anylistfromlistoflists <- listoflists, element<-anylistfromlistoflists, elem >= 3, z <- someotherlist] References arent missing. They are implemented under both the ST and IO monads. sprintf ... show ?? (still show peruses no format specifiers so it can be kinda blah.) (!!) extracts a char from String since type String = [Char] oh, and it isnt missing those math functions either. Take another look at the Prelude (google search it as I'm to lazy to find out url for exact page in haskell 98 report) .... Oops, I see that "missing:" in your page really doesnt mean missing from language. A number of the "missing:" things (esp the math) can be had by just looking at the Haskell Report. a google search "Haskell 98 Report Prelude" probably gets you there. You Have quite a list of languages there. Seems like I've come upon your page before. I'm sure there'll be many more to bookmark it and use it. Jay Cox

ketil@ii.uib.no (Ketil Z. Malde) writes: [...]

The . operator is used for package scope when packages (modules) are imported "qualified".

ok

Indentation can optionally be replaced by { ; and }.

ok

In addition to . function composition, there's also $ function application, which often is more practical to use.

I could put it in "grouping expressions": $ ... Haskell WDYT?

Under "control flow", there's also

case x of v0 -> e0 v1 -> e1 ... otherwise -> e

ok

and

| bool0 = e0 | bool1 = e1 | ... | otherwise = en

i put this one in category "if_then_else" (just like Lisp's "cond") uh... how can this be one-line written?

I'm not sure if "iterate" counts as loop forever?

I don't think there can be a "loop forever" construct in haskell? in OCaml, it is simply: let loop(f) = f() ; loop(f) and is only useful together with exceptions and side-effects.

I can't remember any %-based sprintf off the top of my head, but hey, who'd want one anyway?

me! I've always wondered how you internationalize a program without it? eg: "This encryption key is too simple (must be at least %d characters long)" "The package %s needs to be installed. Do you want to install it?" (I agree you don't need the full power of sprintf for this)

(!!) accesses an indexed character

ok

As for "duplicate n times", I suppose you'll have to combine the two Prelude functions (concat . repeat n), while (map toUpper)/(map toLower) converts the case of strings, , and substrings of lenght l at position i can be extracted by (take l . drop i). (Remember that strings are lists!)

i don't put any non-simple functions, the main aim is not to show how it can be done, but what are the various names used in various languages.

Dictionaries can (inefficiently in some cases) be constructed using assoc lists, with the "lookup" function as accessor.

there's a special entry for it: 'lookup an element in a association list' Thanks!

Pixel writes:

...

In addition to . function composition, there's also $ function application, which often is more practical to use.

I could put it in "grouping expressions":

$ ... Haskell

Yes, but that might apply to the . operator too. But yes, essentially it replaces parentheses.

...

| bool0 = e0 | bool1 = e1 | ... | otherwise = en

i put this one in category "if_then_else" (just like Lisp's "cond")

Yes, "cond" is exactly what it is, I think.

uh... how can this be one-line written?

Well, it needs to be part of something more, e.g. isZero x | x==0 = True | otherwise = False

...

I can't remember any %-based sprintf off the top of my head, but hey, who'd want one anyway?

me! I've always wondered how you internationalize a program without it?

That's easy - I don't :-) -kzm -- If I haven't seen further, it is by standing in the footprints of giants

[...]

(I guess its a cousin to templates in C++) Or perhaps you need a separate section for syntax for constructing new datatypes..

yes, i think so. With enums and ranges being a special case. i'll also put records [...]

(Please dont take this as an insult by my re-explaining these things. I just want to make myself clear.)

the pb is that the semantic is so different between the languages. So i just put all of them with no explaination.

...

...

Under constrol structure, at least give mention to monads! Common examples (ST,IO,List,Maybe) and "do notation"

Monads are defined by instanciating them under the Monad type class. (basically giving definitions for the operators >>= (aka 'bind') and >>

please be more precise, what do i put? in which category?

I guess I suggested control structure because in a way, you can "control the flow" from a semantic point of view of your program by building / choosing a specific monad. For instance, usage of the List monad brings nondeterminism into the language (although, in reality, the multiple solutions alluded to by the term are elements of a deterministically (is that a word?!) produced list)

"syntax across languages" is about syntax! If something needs much explaination, it can't be included :p [...]

I suppose a sollution to what to do with do-notation is to put something like [...] or do {stmnt; var <-stmtn; etc}

under your section named "Various Operators" with description "do statments under monad"

I don't accept entries where only one language fits in :p (this may change as soon as monads appear in more languages) [...]

...

...

References arent missing. They are implemented under both the ST and IO monads.

what is the syntax?

no syntax, only functions which create/manipulate them (under some monad).

do{ x<-newSTRef exp; y <-readSTRef x; writeSTRef x exp}

for IORefs do s/ST/IO/g to above line.

eurk ERROR "/usr/share/hugs/lib/exts/ST.hs":48 - Syntax error in type expression (unexpected `.') isn't there a way ST.hs would require the extensions? a pragma or something? someone not knowing the "-98" would wonder for a long time about what to do :-( anyway, the simplest examples i found: show $ runST (do { x <- newSTRef 2; writeSTRef x 3 ; readSTRef x }) so i can write: newSTRef in "reference (pointer)" "creation" readSTRef writeSTRef in "reference (pointer)" "dereference" WDYT? PS: show $ runST $ do { x <- newSTRef 2; writeSTRef x 3 ; readSTRef x } is not working :'-(

Being able to specify the extensions required in a source file would be very useful in a range of cases. Very often helping other people with Haskell (in the case where they are trying to use someone else's module) is just a question of saying "try '-98'" or "try '-fglasgow-exts'" or whatever.

ghc and nhc98 already support this. ghc's mechanism is {-# OPTIONS -fglasgow-exts ... etc #-} at the top of the file - but there are quite a few restrictions on what flags are accepted in that pragma. nhc98's mechanism is {-# OPTIONS_COMPILE -nkpat ... etc #-} anywhere in the file, which has no restrictions on the options it accepts - you can use anything that can appear on the commandline. Incidentally, nhc98 also recognises the form {-# OPTIONS_LINK -L/usr/local/lib -lreadline ... etc #-} for extra link options, which are accumulated from all modules specified on the commandline. Regards, Malcolm

On Tue, 12 Feb 2002 14:43:22 +0000, Malcolm Wallace wrote:

...

Being able to specify the extensions required in a source file would be very useful in a range of cases. Very often helping other people with Haskell (in the case where they are trying to use someone else's module) is just a question of saying "try '-98'" or "try '-fglasgow-exts'" or whatever.

ghc and nhc98 already support this. [...]

Ah, thanks. I appeal to everyone distributing Haskell libraries to use them, then :-) Cheers, Ganesh