Hi, Are there any programs to strip comments and blank lines from a Haskell source file, that work on normal and literate programs? Thanks. -- Nick Nethercote njn25@cam.ac.uk

Cagdas Ozgenc wondered: | Is there a reason why partial application cannot be | applied in arbitrary order? Was it a technical | difficulty in the design of Haskell? Or is it just | following beta reduction rigorously? Alastair David Reid answered: | Haskell doesn't dictate any particular evaluation | order. If you look at the name of the Haskell report, | it calls Haskell a "non-strict" language not a "lazy" | language. Somehow I do not think that Cagdas was talking about evaluation order at all. I think he referred to the following: Suppose I have a function f which is defined to have 3 arguments: f x y z = ... Now, when I want to partially apply f to two arguments, say 1 and 2, I can say this: ... (f 1 2) ... However, if I want to leave out the middle argument, I have to say: ... (\y -> f 1 y 3) ... And, similarly, for the first one: ... (\x -> f x 2 3) ... This seems rather ugly, since the order of arguments in a function plays a crucial role. For example, the map function takes the list as its second argument, since it is so much more common to partially apply map with the function rather than the list. For 2-argument functions, the sections notation might help: (1 `f`) -- === (f 1) === (\y -> f 1 y) (`f` 2) -- === (\x -> f x 2) In a distant past, Erik Meijer and I experimented with introducing the syntax: (f 1 2 _) (f 1 _ 3) (f _ 2 3) But it became all very clumsy. Regards, /Koen. -- Koen Claessen http://www.cs.chalmers.se/~koen Chalmers University, Gothenburg, Sweden.

Koen Claessen writes: [...]

... (\x -> f x 2 3) ...

This seems rather ugly, since the order of arguments in a function plays a crucial role. For example, the map function takes the list as its second argument, since it is so much more common to partially apply map with the function rather than the list.

For sure the order of arguments play a crucial role in MLs. I don't know many other syntax: - merd http://merd.net/choices_syntax.html#function_calls f(1, 2, ) is (f 1 2) f(, 2, 3) is (\x -> f x 2 3) - OCaml's labels http://caml.inria.fr/ocaml/htmlman/manual006.html f ~y:2 ~z:3 is (\x -> f x 2 3) - Pop-11 http://www.cs.bham.ac.uk/research/poplog/primer/node96.html f(% 2, 3 %) is (\x -> f x 2 3) I'm interested in other syntaxes...

For 2-argument functions, the sections notation might help:

(1 `f`) -- === (f 1) === (\y -> f 1 y) (`f` 2) -- === (\x -> f x 2)

I never thought of this :) Of course it also works with more than 2-argument functions when you want to partially apply only the 2 second argument: (`f` 2) 1 3

In a distant past, Erik Meijer and I experimented with introducing the syntax:

(f 1 2 _) (f 1 _ 3) (f _ 2 3)

But it became all very clumsy.

do you have more info on this?

Cagdas Ozgenc:

That's right. I was thinking of the following syntax. I orginally had the idea for C++, where you can't do partial application at all.

f x y z=...

f # 3 4

omitting the first parameter, and ....

Array languages with true multidimensional arrays often have a this kind of syntax to extract subarrays, for instance A(*,J) or A(,J) to extract column J from the matrix A. Now, if you think about arrays as partial functions from indices to values, then row J of matrix A is precisely \I -> A(I,J). This syntax can be very convenient for array computations. Björn Lisper

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"Cagdas" == Cagdas Ozgenc writes:

Cagdas> Koen Claessen contributed:

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Somehow I do not think that Cagdas was talking about evaluation order at all. I think he referred to the following: Suppose I have a function f which is defined to have 3 arguments:

Cagdas> That's right. I was thinking of the following syntax. I orginally had the Cagdas> idea for C++, where you can't do partial application at all. Cagdas> f x y z=... Cagdas> f # 3 4 As another note on the subject, this is similar to SRFI 26 for Scheme which can be found at: http://srfi.schemers.org/srfi-26/ -- Cheers =8-} Mike Friede, Völkerverständigung und überhaupt blabla