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Show HN: a Lisp that uses JSON instead of S-expressions (in .js)

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Re: Show HN: a Lisp that uses JSON instead of S-expressions (in .js)

#51

Post by anghyflawn »

akkartik wrote: post #45
arethuza wrote: post #4

I really like Lisp (I was even paid to develop in it for 6 years) and these days I love JSON because of its Lisp-ish nature - but those expressions look damn ugly to me.

You could lose the quotes around strings, but you'd still have the commas. Maybe start with lisp and just add {key: value key2: value2} syntax for tables? It'd be useful to get ruby-style keyword args for free, at least. I spend a lot of time thinking about keyword args because I've been working on a lisp interpreter that supports them. Here's a webserver that is nice to read because of a crucial keyword arg (it star…

What's wrong with Common Lisp's keyword arguments? I'm not being snarky, just asking. I'd say CL works at least as well as Python in this respect.

Re: Show HN: a Lisp that uses JSON instead of S-expressions (in .js)

#52

Post by lisper »

baddox wrote: post #48
lisper wrote: post #19

Earlier quoted context omitted.

This presents a very thorny language design problem. Lists have this very nice property that they are ordered , which lets you attach implied semantics to the position of an element, e.g.: (defun foo (a b c) ...) We know this is a function defining because the symbol DEFUN is in the FIRST position of the list. Associative arrays are unordered, so you have to explicitly label everything: { top-level-form : defun, argu…

> Associative arrays are unordered That's not true in general, is it? It's just hash maps that are unordered. You can use a tree to represent an associative array (so the order of keys is found by a tree traversal), or a "worse" method like an association list (linked list). You can also just store a linked list of keys along with your hash map.

You are conflating the abstract data type with its implementation. A hash-map is one implementation of an associative array. A tree is another implementation of an associative array. A tree happens to depend on an ordering of the keys in order to do efficient lookup and a hash-map doesn't, but this is an implementation detail. It's not part of the definition of an associative array. And this is a good thing because not all data types have well defined orderings but you still might want to use them as keys, with symbols being the most notable example.

Re: Show HN: a Lisp that uses JSON instead of S-expressions (in .js)

#53

Post by arethuza »

akkartik wrote: post #45
arethuza wrote: post #4

I really like Lisp (I was even paid to develop in it for 6 years) and these days I love JSON because of its Lisp-ish nature - but those expressions look damn ugly to me.

You could lose the quotes around strings, but you'd still have the commas. Maybe start with lisp and just add {key: value key2: value2} syntax for tables? It'd be useful to get ruby-style keyword args for free, at least. I spend a lot of time thinking about keyword args because I've been working on a lisp interpreter that supports them. Here's a webserver that is nice to read because of a crucial keyword arg (it star…

Common Lisp already has hashtables (not to mention simple association lists) what it doesn't have is a standard syntax for them. However, this is pretty easy to add with reader macros, for example:

http://frank.kank.net/essays/hash.html

Re: Show HN: a Lisp that uses JSON instead of S-expressions (in .js)

#54

Post by akkartik »

lisper wrote: post #50
akkartik wrote: post #40

Earlier quoted context omitted.

"Extant Lisps collect vectors just fine." But they don't permit pointers inside the vectors, do they? I think if you permit internal pointers so you can have copyless cdr, computing reachability would get really expensive.

The phrase "permit pointers inside the vectors" doesn't really make sense. Vectors are just ordered collections of objects. They don't have insides and outsides, except insofar as the objects contained by the vector could be (but usually aren't) considered "inside" the vector. Lisp vectors are usually implemented as arrays of pointers, so in that sense pointers are "permitted" inside vectors. But I'm guessing that's…

  (a (b (c . nil))
  ^  ^
  |  |
  |  |
  A  B
If you implement lists as vectors with car/cdr (I'm still thinking about your other questions) and choose to have cdr not copy results out of the original cell, you can end up in the (rope-like) situation above with pointer B (value (b c)) in addition to pointer A (value (a b c)). But that makes GC inefficient. For a vector to be GC'd you have to know what internal pointers it has, and then you have to make the choice to copy them out if they're 'toward the end', or to leave the vector uncollected.

(ignore pointers to a, b, and c.)

Re: Show HN: a Lisp that uses JSON instead of S-expressions (in .js)

#55

Post by akkartik »

anghyflawn wrote: post #51
akkartik wrote: post #45

Earlier quoted context omitted.

You could lose the quotes around strings, but you'd still have the commas. Maybe start with lisp and just add {key: value key2: value2} syntax for tables? It'd be useful to get ruby-style keyword args for free, at least. I spend a lot of time thinking about keyword args because I've been working on a lisp interpreter that supports them. Here's a webserver that is nice to read because of a crucial keyword arg (it star…

What's wrong with Common Lisp's keyword arguments? I'm not being snarky, just asking. I'd say CL works at least as well as Python in this respect.

No, in Common Lisp you can't mix a keyword arg for a non-keyword param, or vice versa.

Re: Show HN: a Lisp that uses JSON instead of S-expressions (in .js)

#56

Post by spacemanaki »

akkartik wrote: post #45
arethuza wrote: post #4

I really like Lisp (I was even paid to develop in it for 6 years) and these days I love JSON because of its Lisp-ish nature - but those expressions look damn ugly to me.

You could lose the quotes around strings, but you'd still have the commas. Maybe start with lisp and just add {key: value key2: value2} syntax for tables? It'd be useful to get ruby-style keyword args for free, at least. I spend a lot of time thinking about keyword args because I've been working on a lisp interpreter that supports them. Here's a webserver that is nice to read because of a crucial keyword arg (it star…

> Maybe start with lisp and just add {key: value key2: value2} syntax for tables? It'd be useful to get ruby-style keyword args for free, at least.

This is how Clojure hacks around keyword args, and altho destructuring kind of makes up for it, it's not that pretty. (It's not pretty in Ruby either) Hash table literals are a nice addition to Lisp but I think it's kind of ugly to use them for keyword args.

Re: Show HN: a Lisp that uses JSON instead of S-expressions (in .js)

#57

Post by akkartik »

spacemanaki wrote: post #56
akkartik wrote: post #45

Earlier quoted context omitted.

You could lose the quotes around strings, but you'd still have the commas. Maybe start with lisp and just add {key: value key2: value2} syntax for tables? It'd be useful to get ruby-style keyword args for free, at least. I spend a lot of time thinking about keyword args because I've been working on a lisp interpreter that supports them. Here's a webserver that is nice to read because of a crucial keyword arg (it star…

> Maybe start with lisp and just add {key: value key2: value2} syntax for tables? It'd be useful to get ruby-style keyword args for free, at least. This is how Clojure hacks around keyword args, and altho destructuring kind of makes up for it, it's not that pretty. (It's not pretty in Ruby either) Hash table literals are a nice addition to Lisp but I think it's kind of ugly to use them for keyword args.

Ah, that's good to know, thanks.

Re: Show HN: a Lisp that uses JSON instead of S-expressions (in .js)

#58

Post by lisper »

akkartik wrote: post #54
lisper wrote: post #50

Earlier quoted context omitted.

The phrase "permit pointers inside the vectors" doesn't really make sense. Vectors are just ordered collections of objects. They don't have insides and outsides, except insofar as the objects contained by the vector could be (but usually aren't) considered "inside" the vector. Lisp vectors are usually implemented as arrays of pointers, so in that sense pointers are "permitted" inside vectors. But I'm guessing that's…

(a (b (c . nil)) ^ ^ | | | | A B If you implement lists as vectors with car/cdr (I'm still thinking about your other questions) and choose to have cdr not copy results out of the original cell, you can end up in the (rope-like) situation above with pointer B (value (b c) ) in addition to pointer A (value (a b c) ). But that makes GC inefficient. For a vector to be GC'd you have to know what internal pointers it has,…

Ah. What you are calling a "pointer to the inside of a vector" is actually called a displaced vector. It's a standard Common Lisp feature, and no problem for modern GCs.

Re: Show HN: a Lisp that uses JSON instead of S-expressions (in .js)

#59

Post by arethuza »

akkartik wrote: post #55
anghyflawn wrote: post #51

Earlier quoted context omitted.

What's wrong with Common Lisp's keyword arguments? I'm not being snarky, just asking. I'd say CL works at least as well as Python in this respect.

No, in Common Lisp you can't mix a keyword arg for a non-keyword param, or vice versa.

Couldn't you write a macro to call functions using whatever mixture of keyword and non-keyword params you wanted?

Or perhaps using some CLOS magic do to do this behind the scenes, e.g. no-applicable-method

http://www.lispworks.com/documentation/HyperSpec/Body/f_no_a...

[NB It's been a long time since I did much Lisp]

Re: Show HN: a Lisp that uses JSON instead of S-expressions (in .js)

#60

Post by wanorris »

lisper wrote: post #52
baddox wrote: post #48

Earlier quoted context omitted.

> Associative arrays are unordered That's not true in general, is it? It's just hash maps that are unordered. You can use a tree to represent an associative array (so the order of keys is found by a tree traversal), or a "worse" method like an association list (linked list). You can also just store a linked list of keys along with your hash map.

You are conflating the abstract data type with its implementation. A hash-map is one implementation of an associative array. A tree is another implementation of an associative array. A tree happens to depend on an ordering of the keys in order to do efficient lookup and a hash-map doesn't, but this is an implementation detail. It's not part of the definition of an associative array. And this is a good thing because n…

I think the mistake the parent post has made is conflating the kind of ordering you're referring to -- ordering in a tree implementation to allow for O(log n) resolution -- and ordering to preserve the position of each key-value pair as it was in the source structure. These are only the same thing if the source structure already happens to be sorted by some kind of ordering, something that obviously cannot be extended to the general case of preserving positionality.

AFAIK, the only two ways to preserve positionality as part of an associative array are (1) to store as a postional list of key-value pairs and use linear search to find matching keys, or (2) to use an additional data structure as an index, either by storing as a positional list and having a additional map from key value into the positions, or by storing as a map and having an additional list of keys stored in positional ordering.

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