spacemanaki on Examples of Lisp formatting through history

Comment on Examples of Lisp formatting through history parent

That seems pretty strange, and some of those examples are really hard to read. Care to share some real Lisp code and not just (a (b (c ... ))) examples? And maybe some motivating examples in Haskell? I just can't see how any of these are an improvement and I'm curious.

hollerith 14y

In Haskell it is not uncommon to see things like

  foo x y = x >>= \a -> case a of
    Leaf -> ..
    Branch aleft aright -> ..

which translates into the Scheme pseudocode

  (define (foo x y) (bind x (lambda (a) (case a
    ((leaf) ..)
    (branch aleft aright) ..)

Although such an indentation pattern (namely, multiple "unclosed" open parens on one line, which all get closed at once) is very uncommon in Scheme or Lisp code, I find it handy enough to trade off for certain other "competing" indentation patterns (namely, the one in the final example in grandparent) traditional in Scheme and Lisp.

I have been meaning to put my .emacs.d (5800 lines) on Github. Do you want me to email you when I have done so?

dan00 14y

    foo x y = x >>= \a -> case a of
        Leaf -> ..
        Branch aleft aright -> ..

Hanging lambdas yes, but I don't see the advantage of putting the beginning of the case into the same line.

    foo x y = x >>= \a ->
        case a of
             Leaf                -> ..
             Branch aleft aright -> ..

But the example is a bit contrived, because you could write it this way:

    foo x y = do
        a <- x
        case a of
             Leaf                -> ..
             Branch aleft aright -> ..

hollerith 14y

We must have different goals for our choice of indentation style: my goal is to minimize lines of code while preserving readability.

(Not lining things up as in

  (f xxx
    yyy)

initially detracts from readability, but in my experience with the new style, readability goes back up to very close to where it was as I get used to the new style.)

eru 14y

I actually like the first one best, and would prefer a case-lambda even more. Once it becomes available we can write

  foo x y = x >>= \case
    Leaf -> ..
    Branch l r -> ..

modulo whatever syntax gets chosen. That would save an unnecessary temporary variable. (See https://groups.google.com/group/haskell-cafe/browse_thread/t...)

Temporary variables clutter up the name space. While reading code you have to look for shadowing, or whether that variable is ever used again.

hollerith 14y

Agree about case lambda (and consequently that I could have chosen a better example).

spacemanaki 14y

That makes much more sense given the snippet of Haskell and isn't so hard to read. No need to email though, I'm pretty happy with the standard Lisp indentation style. Thanks for clarifying.

hollerith 14y

You are welcome.

By the way, any Emacker who shares my skepticism of the value of the traditional Emacs practice of having special indentation amounts for certain special forms and who prefers a slightly more regular/boring indentation style can get the TAB key to reflect that skepticism/preference with (setq lisp-indent-offset 2) and (setq lisp-body-indent 2) (or (setq lisp-indent-offset 4) and (setq lisp-body-indent 4) or such).

Disclaimer: untested on Emacs 23 or 24. (I'm still on Emacs 22.)

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