5 ms·

Lisp after Python after Lisp

70 points by thepanister 18y ago

jimbokun 18y 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 18y ago
  on python - not anymore, since 2.5 (probably earlier) you can do: (x if cond else y) which is essentially (cond ? x : y)
  - jimbokun 18y ago
    Definite improvement! Thanks for the information.
    - jcausey 18y ago
      The previous ternary hack in Python (which was still relatively elegant) was: a = ("False", "True")[condition] It's a little fugly -- but if you know the basic semantics of Python, it's quite readable. It is nice that we have a proper ternary now, though.
      - EliAndrewC 18y ago
        Actually I think the more common hack was a = cond and x or y which had the downside that if the second part (in this case x) evaluates to False then a ends up equal to y even through that's not what you were trying to do. Sometimes this is a problem and sometimes not, but it's been irrelevant for the past few years.
        jcausey 18y ago
        Very true. I've seen that hack before, but I guess I mentally settled on my first example (probably due to the irksome possibility of x=0\False). Unfortunately, there were probably more hacks than our two examples. Thank goodness Guido (etc) settled on a real ternary semantic -- we were heading into Perl more-than-9000-ways-to-do-something territory!
- bk 18y 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 18y 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.
danprager 18y 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 18y ago
  Instead of declaring a local function, you can use let (http://docs.plt-scheme.org/reference/let.html http://docs.plt-scheme.org/reference/let.html) e.g.: > (let fac ([n 10]) (if (zero? n) 1 (* n (fac (sub1 n))))) 3628800
  - danprager 18y ago
    Yes, "named let" is lovely, but perhaps less obvious for the non-cognoscenti. It also doesn't translate into Python, etc.
- jamongkad 18y ago
  What do you mean by this? Is this the same method of declaring inner functions within the scope of the outer function?
  - smanek 18y 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).
  - danprager 18y 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).

70 points by thepanister 18y 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 18y ago
on python - not anymore, since 2.5 (probably earlier) you can do: (x if cond else y) which is essentially (cond ? x : y)
- jimbokun 18y ago
  Definite improvement! Thanks for the information.
  - jcausey 18y ago
    The previous ternary hack in Python (which was still relatively elegant) was: a = ("False", "True")[condition] It's a little fugly -- but if you know the basic semantics of Python, it's quite readable. It is nice that we have a proper ternary now, though.
    - EliAndrewC 18y ago
      Actually I think the more common hack was a = cond and x or y which had the downside that if the second part (in this case x) evaluates to False then a ends up equal to y even through that's not what you were trying to do. Sometimes this is a problem and sometimes not, but it's been irrelevant for the past few years.
      - jcausey 18y ago
        Very true. I've seen that hack before, but I guess I mentally settled on my first example (probably due to the irksome possibility of x=0\False). Unfortunately, there were probably more hacks than our two examples. Thank goodness Guido (etc) settled on a real ternary semantic -- we were heading into Perl more-than-9000-ways-to-do-something territory!
bk 18y 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 18y 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.

danprager 18y 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 18y ago
Instead of declaring a local function, you can use let (http://docs.plt-scheme.org/reference/let.html http://docs.plt-scheme.org/reference/let.html) e.g.: > (let fac ([n 10]) (if (zero? n) 1 (* n (fac (sub1 n))))) 3628800
- danprager 18y ago
  Yes, "named let" is lovely, but perhaps less obvious for the non-cognoscenti. It also doesn't translate into Python, etc.
jamongkad 18y ago
What do you mean by this? Is this the same method of declaring inner functions within the scope of the outer function?
- smanek 18y 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).
- danprager 18y 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).