4 ms·

- you can make your own domain specific language in Lisp (e.g. imagine that you want to create a custom 'for' statement, or some kind of a new pattern matching

- you can make your own domain specific language in Lisp (e.g. imagine that you want to create a custom 'for' statement, or some kind of a new pattern matching operator) - you can easily write programs that edit themselves

jedimastert 7y ago
I see both of those things a lot. The problem is if you aren't already familiar with those idea, the statements mean literally nothing. They basically don't make sense.
- ken 7y ago
  These examples aren't so far out there. DSLs exist in other languages. Statements exist in other languages. A programmer who has never used macros can imagine being able to create these, even if they have no idea what exactly that would look like in a Lisp program. That issue is also true of any game-changing technology you haven't used yet. If you hadn't used a personal computer, we could enumerate the features and advantages, but you probably wouldn't be able to truly appreciate it until you used one yourself.
- AlexCoventry 7y ago
  They're also rarely useful things to do in regular software development.
  - quickthrower2 7y ago
    I wonder if we struggle needlessly though in "regular software development" - and entire jobs or teams exist because we didn't find the right way to express things in a language. OTOH you could create lisp code that is so unique and weird in it's semantics that it's hard for a new team member to get onboard. But I've seen that done in C# too which allows you to have code that writes code at runtime (not as elegantly though!).
    - AlexCoventry 7y ago
      Yeah, writing your own language and self-modifying code can give you a lot of leverage, but usually they also make the code so much harder for other people to pick up that it's not worth it.
- FrozenVoid 7y ago
  The idea is that all LISP code is data that is easily altered, essentially https://en.wikipedia.org/wiki/Abstract_syntax_tree https://en.wikipedia.org/wiki/Abstract_syntax_tree encapsulated in parens. LISP syntax is uniform,everything(functions,data,argument lists) is nested lists of lists like (list(list(list))), so that allows altering specific places "in-the-list"(place 1,2,3...) as form of meta-programming, where normal syntax FOR( A IN B) would be written roughly as (for a b) where for is used as a function taking 'a' and 'b' as parameters, but in this form(where 'for' is just the first element of the list) you can have functions that "alter-the-list" by example (replace-first-list-element (for a b) replacement-part) returns (replacement-part a b).
bogdanoff_2 7y ago
What is the second bullet point referring to?
- shaftway 7y ago
  Lisp syntax in a nutshell is: "(" {function} [" " {argument}...] ")" If you don't want to actually run a function, like you just want a list of values, you put a single quote before it: "'(" [{item} [" " {item}...]] ")" So if you want to do `(1 + 2) * 3` it'd be `(* (+ 1 2))`. Parentheses abound. On top of that everything is a function, including if statements, assignment, and even how you define a new function. So factorial in lisp is: (defun factorial (x) (if (<= x 0) 1 (* x (factorial (- x 1))) ) ) You'll notice that it ended with 5 close-parentheses. Different people have different strategies for managing that along with indents and newlines.
thiht 7y ago
Second point sounds like a nightmare
pgcj_poster 7y ago
> you can easily write programs that edit themselves Hah! I can do that too: #!/usr/bin/env python3 # # script.py # Copyright 2019 pgcj_poster print('Hello World') with open('script.py', 'w') as f: f.write(f.read().replace('Hello World', 'Goodbye World')) Clearly Lisp is of no use in 2019.
- contravariant 7y ago
  You should use '__file__' for increased generality. Note that you can also import a module and refer to its location on disk as 'module.__file__'. I may or may not have used this to modify a few core python modules in place.

jedimastert 7y ago

I see both of those things a lot. The problem is if you aren't already familiar with those idea, the statements mean literally nothing. They basically don't make sense.

ken 7y ago
These examples aren't so far out there. DSLs exist in other languages. Statements exist in other languages. A programmer who has never used macros can imagine being able to create these, even if they have no idea what exactly that would look like in a Lisp program. That issue is also true of any game-changing technology you haven't used yet. If you hadn't used a personal computer, we could enumerate the features and advantages, but you probably wouldn't be able to truly appreciate it until you used one yourself.
AlexCoventry 7y ago
They're also rarely useful things to do in regular software development.
- quickthrower2 7y ago
  I wonder if we struggle needlessly though in "regular software development" - and entire jobs or teams exist because we didn't find the right way to express things in a language. OTOH you could create lisp code that is so unique and weird in it's semantics that it's hard for a new team member to get onboard. But I've seen that done in C# too which allows you to have code that writes code at runtime (not as elegantly though!).
  - AlexCoventry 7y ago
    Yeah, writing your own language and self-modifying code can give you a lot of leverage, but usually they also make the code so much harder for other people to pick up that it's not worth it.
FrozenVoid 7y ago
The idea is that all LISP code is data that is easily altered, essentially https://en.wikipedia.org/wiki/Abstract_syntax_tree https://en.wikipedia.org/wiki/Abstract_syntax_tree encapsulated in parens. LISP syntax is uniform,everything(functions,data,argument lists) is nested lists of lists like (list(list(list))), so that allows altering specific places "in-the-list"(place 1,2,3...) as form of meta-programming, where normal syntax FOR( A IN B) would be written roughly as (for a b) where for is used as a function taking 'a' and 'b' as parameters, but in this form(where 'for' is just the first element of the list) you can have functions that "alter-the-list" by example (replace-first-list-element (for a b) replacement-part) returns (replacement-part a b).

bogdanoff_2 7y ago

What is the second bullet point referring to?

shaftway 7y ago
Lisp syntax in a nutshell is: "(" {function} [" " {argument}...] ")" If you don't want to actually run a function, like you just want a list of values, you put a single quote before it: "'(" [{item} [" " {item}...]] ")" So if you want to do `(1 + 2) * 3` it'd be `(* (+ 1 2))`. Parentheses abound. On top of that everything is a function, including if statements, assignment, and even how you define a new function. So factorial in lisp is: (defun factorial (x) (if (<= x 0) 1 (* x (factorial (- x 1))) ) ) You'll notice that it ended with 5 close-parentheses. Different people have different strategies for managing that along with indents and newlines.

thiht 7y ago

Second point sounds like a nightmare

pgcj_poster 7y ago

> you can easily write programs that edit themselves Hah! I can do that too: #!/usr/bin/env python3 # # script.py # Copyright 2019 pgcj_poster print('Hello World') with open('script.py', 'w') as f: f.write(f.read().replace('Hello World', 'Goodbye World')) Clearly Lisp is of no use in 2019.

contravariant 7y ago
You should use '__file__' for increased generality. Note that you can also import a module and refer to its location on disk as 'module.__file__'. I may or may not have used this to modify a few core python modules in place.