Lisp after Python after Lisp

http://devlog.bigmonachus.org/2009/03/lisp-after-python-after-lisp.html

by thepanister • 17 years ago

70 17 17 years ago

devlog.bigmonachus.org

jimbokun2• 17 years ago

"I don't know if there are programmers out there whose pseudo-language is functional. Maybe it's just human nature to think imperatively."

A lot of time it just kills me that "if" statements don't default to returning the true branch or false branch. You need the ternary conditional operator in Java and other C-derivatives, and in Python you need to resort to some hack with and/or precedence.

I'm also wondering if I should declare all variables final in Java, and only change that default if I really, really have to.

vang3lis• 17 years ago

on python - not anymore, since 2.5 (probably earlier) you can do:

(x if cond else y) which is essentially (cond ? x : y)

jimbokun2• 17 years ago

Definite improvement! Thanks for the information.

bk• 17 years ago

I guess that's why Ruby has been called an "acceptable lisp". I take "everything is an expression" so for granted by now, and it makes for beautiful, terse code.

The non-working python if statement/assignment example from the article works perfectly fine in Ruby. (No python/ruby flamewar please, that's really not the point)

arohner• 17 years ago

How about a ruby/lisp flamewar? :-) J/K.

In all seriousness though, I've recently moved to Clojure from Ruby. I'm not looking back. Clojure is significantly cleaner, faster, and has better libraries than Ruby.

danprager4• 17 years ago

Learning Scheme helped my Python by teaching me some new (to me) idioms, besides the first-class function stuff.

For example, it is natural in Scheme to declare a lot of local information, including local function definitions. These have the great advantage of knowing about variables within the local environment. So rather than declaring an external function with heaps of parameters to pass in local state, you just declare a local function which automatically gets access to the variables in the surrounding scope.

The same idiom works neatly in Python too, but didn't occur to me previously.

* * *

Also after learning Python and Scheme, Ruby felt a bit like a cross between the two, and quite comfortable.

antiismist• 17 years ago

Instead of declaring a local function, you can use let (http://docs.plt-scheme.org/reference/let.html)

e.g.:

  > (let fac ([n 10])
      (if (zero? n)
          1
          (* n (fac (sub1 n)))))

  3628800

danprager4• 17 years ago

Yes, "named let" is lovely, but perhaps less obvious for the non-cognoscenti. It also doesn't translate into Python, etc.

jamongkad3• 17 years ago

What do you mean by this? Is this the same method of declaring inner functions within the scope of the outer function?

smanek• 17 years ago

Pretty much. The trick is that since scheme is a lisp-1 there is no need for a different special operator to signify you're declaring a local function instead of a local variable (a la the flet/let dichotomy).

danprager4• 17 years ago

Yes, in that case the inner function has access to the arguments of the outer function. But you can go deeper -- e.g. declaring an inner function inside code inside the out er function -- which also knows about the local variables in the outer function.

Or if you're only doing it once use a lambda (with the same advantages).

Lisp after Python after Lisp

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