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I may be perceiving this wrong, but it appears to me that in more recently newly created languages lexical scoping and explicit variable declaration are conspic

I may be perceiving this wrong, but it appears to me that in more recently newly created languages lexical scoping and explicit variable declaration are conspicuously absent. In the face of these features' positive effects on software quality and maintainability, i have to suspect that their lack is usually a conscious decision. However, probably due to my inexperience in creating programming languages, i cannot think of reasons for this kind of decisions. What could these be?

gagege 12y ago
I'm no language designer either, but I would guess that since Crystal wants to be 100% type inferred, they feel that having to type "var" or "let" is just boilerplate.
- eudox 12y ago
  That has nothing to do with the scoping. There's no way to know whether "left = right" means "Set 'left' to 'right'" or "Create a new variable 'left', with value 'right'".
  - Igglyboo 12y ago
    How are they different? Both produce the same end result, Python manages this syntax just fine.
    - exogen 12y ago
      "Just fine" is papering over the fact that people get tripped up by this in Python all the time – sometimes you need to use the `global` or `nonlocal` statements to resolve the ambiguity. https://docs.python.org/3/reference/simple_stmts.html#global https://docs.python.org/3/reference/simple_stmts.html#global https://docs.python.org/3/reference/simple_stmts.html#nonlocal https://docs.python.org/3/reference/simple_stmts.html#nonloc... Classic example: http://stackoverflow.com/questions/9264763/unboundlocalerror-in-python http://stackoverflow.com/questions/9264763/unboundlocalerror... If you search for UnboundLocalError on StackOverflow, there are 918 results. Not all of them are due to this particular scoping ambiguity, but many of them are.
    - lmm 12y ago
      It's a mistake even in Python. It makes typos harder to catch. And a visible distinction between variables that change and values that don't makes code much easier to reason about.
- axiomabsolute 12y ago
  Even in type inferred languages they serve some use, namely in avoiding mis-typed variable names. Languages which require "var" make a distinction between the intent of declaring a new variable vs setting the value of an existing variable, and so are able to catch instances where the programmer tries to set a non-existent variable.
  - vorg 12y ago
    Or more tersely use := and = to distinguish them.
chrisseaton 12y ago
I can't think of any recently-designed languages that do not have lexical scoping - can you? I'm not sure I can think of any languages at all that have dynamic scoping since the early lisps.
- Igglyboo 12y ago
  The only ones I can think of are Python and Javascript, both were created in the 90's.
  - chrisseaton 12y ago
    Python and JavaScript both have lexical scoping - e.g. http://www.ecma-international.org/ecma-262/5.1/#sec-10.2 http://www.ecma-international.org/ecma-262/5.1/#sec-10.2.
    - Igglyboo 12y ago
      Ah my mistake then, I must be misunderstanding what lexical scoping is.
- axiomabsolute 12y ago
  Features like Scala's implicit parameters could be argued to be a kind of "dynamic scope". True, the language is lexically scoped and most code is written expecting that, but it does allow you to "opt out" of this scoping mechanism and look for values to be specified in the environment.
- marktangotango 12y ago
  Perl my/our/local is the most unusual scoping I know of[1]. But still lexical, except maybe local which is more like an alias? [1] http://www.perlmonks.org/?node_id=66677 http://www.perlmonks.org/?node_id=66677
  - tripa 12y ago
    my is lexical, our is global, local is dynamic.
riffraff 12y ago
> In the face of these features' positive effects on software quality and maintainability are you sure about this for explicit variable declaration? In my experience the problem is more with autovivification than with declaration-is-initialization.
smrtinsert 12y ago
One mans maintainability is another mans mess.

gagege 12y ago

I'm no language designer either, but I would guess that since Crystal wants to be 100% type inferred, they feel that having to type "var" or "let" is just boilerplate.

eudox 12y ago
That has nothing to do with the scoping. There's no way to know whether "left = right" means "Set 'left' to 'right'" or "Create a new variable 'left', with value 'right'".
- Igglyboo 12y ago
  How are they different? Both produce the same end result, Python manages this syntax just fine.
  - exogen 12y ago
    "Just fine" is papering over the fact that people get tripped up by this in Python all the time – sometimes you need to use the `global` or `nonlocal` statements to resolve the ambiguity. https://docs.python.org/3/reference/simple_stmts.html#global https://docs.python.org/3/reference/simple_stmts.html#global https://docs.python.org/3/reference/simple_stmts.html#nonlocal https://docs.python.org/3/reference/simple_stmts.html#nonloc... Classic example: http://stackoverflow.com/questions/9264763/unboundlocalerror-in-python http://stackoverflow.com/questions/9264763/unboundlocalerror... If you search for UnboundLocalError on StackOverflow, there are 918 results. Not all of them are due to this particular scoping ambiguity, but many of them are.
  - lmm 12y ago
    It's a mistake even in Python. It makes typos harder to catch. And a visible distinction between variables that change and values that don't makes code much easier to reason about.
axiomabsolute 12y ago
Even in type inferred languages they serve some use, namely in avoiding mis-typed variable names. Languages which require "var" make a distinction between the intent of declaring a new variable vs setting the value of an existing variable, and so are able to catch instances where the programmer tries to set a non-existent variable.
- vorg 12y ago
  Or more tersely use := and = to distinguish them.

chrisseaton 12y ago

I can't think of any recently-designed languages that do not have lexical scoping - can you? I'm not sure I can think of any languages at all that have dynamic scoping since the early lisps.

Igglyboo 12y ago
The only ones I can think of are Python and Javascript, both were created in the 90's.
- chrisseaton 12y ago
  Python and JavaScript both have lexical scoping - e.g. http://www.ecma-international.org/ecma-262/5.1/#sec-10.2 http://www.ecma-international.org/ecma-262/5.1/#sec-10.2.
  - Igglyboo 12y ago
    Ah my mistake then, I must be misunderstanding what lexical scoping is.
axiomabsolute 12y ago
Features like Scala's implicit parameters could be argued to be a kind of "dynamic scope". True, the language is lexically scoped and most code is written expecting that, but it does allow you to "opt out" of this scoping mechanism and look for values to be specified in the environment.
marktangotango 12y ago
Perl my/our/local is the most unusual scoping I know of[1]. But still lexical, except maybe local which is more like an alias? [1] http://www.perlmonks.org/?node_id=66677 http://www.perlmonks.org/?node_id=66677
- tripa 12y ago
  my is lexical, our is global, local is dynamic.

riffraff 12y ago

> In the face of these features' positive effects on software quality and maintainability are you sure about this for explicit variable declaration? In my experience the problem is more with autovivification than with declaration-is-initialization.

smrtinsert 12y ago

One mans maintainability is another mans mess.