Automatic Coding

Thoughts on programming, software engineering, and Emacs

Mod Lang

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It occurred to me this week that CoffeeScript is Javascript with modern syntax. The thought appeared unprompted, and I’m not writing here to argue that it’s right or wrong; more that the thought itself gave me pause for thought.

It made me realise that somewhere in my programming brain I was differentiating between ‘old world’ and ‘new world’ syntactic features, and the more I thought, the more interesting the thought was.

So the reason I am writing here is to try to examine what it was about CoffeeScript that prompted the thought, by presenting some syntactic features that, to me, feel ‘modern’. I’ll also try to explain why I think each feature belongs in a modern language.

1. Stabby Lambdas

The obvious number 1. CoffeeScript’s lambda syntax uses the form (arguments) -> body. The style is probably derived from Haskell; Erlang also uses it, and it’s more recently been adopted by Scala, C# and (in a slightly backwards form) Ruby.

What this says about language evolution is obvious, I think: programmers want to use anonymous functions. They want to create them quickly and easily, with a meaningful and noise-free syntax. I’d suggest that this is evidence of the current popularity of functional programming style, which is probably a result of the emerging necessity to program for concurrency. I’d also venture that most programmers using this style are interested less in concurrency (at the hardware level) than in a convenient syntax for working with event-driven systems (as well as a language-level Strategy pattern).

2. Noise Reduction

CoffeeScript makes parentheses optional in many cases (as does Ruby); it also, in certain cases, makes braces for declaring object literals optional; commas separating object key-value pairs and array elements can be replaced with newlines; semicolons as line delimiters are not used; comparison and logical operators can in many cases be replaced with equivalent English words (=== with is, !== with isnt, && with and, || with or, etc.).

To the same effect, CoffeeScript, like Ruby, offers flexibility in conditional expressions, so that unless can be used in place of if not, and any conditional operator can be used postfix, allowing bon mots like return unless x is 5.

This makes the language easy to read. It reads fluently, uninterrupted by messy, alienating punctuation. Sometimes this visual clarity is bought at the expense of semantic clarity, though, and the CoffeeScript compiler can bite you if you’re too laissez-faire. Also, how to ‘phrase’ your code becomes an additional, and possibly unwelcome, decision. Rubyists have long faced these issues, and adherence to the language’s idioms is now nearly as important as correct syntax.

The movement to greater flexibility and fewer sigils seems to have met with more approval than hostility, though, and I’d argue that a driving reason for this is that less noisy, more malleable syntax enables the creation of domain-specific languages. Rails famously leverages Ruby’s syntax to create what amounts to a declarative language to describe things like entity relationships; other frameworks have tried to follow suit and been frustrated by their host language’s lack of flexibility. I won’t name names.

3. Expressiveness through Expressions

In CoffeeScript, As in Ruby, Scala, OCaml, Haskell and Lisp, (almost) everything is an expression. In simple terms, this means that every language construct returns a value. An important consequence of this is implicit returns: because every construct must return a value, all functions must return a value, whether return is called explicitly or not. By default, a function returns the value of the last evaluated expression. This, again, makes for a very concise and expressive syntax, which feels like a function just is its evaluated body:

square = (x) -> x * x

This applies to conditionals too:

x = if true

(Note that this is not ‘idiomatic’ CoffeeScript.)

4. Coalescence

Like Scheme, C#, Ruby, Python and JavaScript, CoffeeScript uses coalescing operators. To JavaScript’s coalescing || and ||=, CoffeeScript adds a coalescing existential operator, ? and ?=. This is particularly useful in combination with the ‘everything is an expression’ behaviour described above:

x = (y if y > 5) or z

It can also be used for simple memoization:

x = null
x ?= -> (i for i in [1..20])

And even to conditionally call a function:

f = (callback) -> callback?()


You may have noticed that most of the languages I’ve mentioned above are some distance from ‘modern’; Scala (released 2003) has the best claim. The others range from early adulthood (Ruby, mid-1990s) to spry seniority (Lisp, late 1950s). Why do aspects of their syntaxes, then, seem to contribute to a sense of modernity in language design?

I think this is quite simple: they don’t look, or act, too much like C.

C is a beautiful language, which does what it’s designed for very well: it interacts with von Neumann-architecture machines at a level appreciably higher than assembly language, whilst being highly performant, small, well-specified, and clear. But it became so popular that the languages that followed it were pretty much required to cargo-cult its syntax. What is Java but a traduction of Smalltalk with C-like syntax bolted on? What is JavaScript but a traduction of Scheme with Java-like syntax bolted on (by mandate, in this case)?

As a result of C’s (and its successors’) popularity, alternative languages like Lisp and Smalltalk rather faded into the background; their practical elements were absorbed, but their syntaxes were repressed. One could argue that Perl brought some of their syntactic ideas closer to the mainstream – I don’t know enough Perl to have an opinion. But once you’ve written Ruby or Python or CoffeeScript, all of them strongly influenced by more humanist languages like the aforementioned, it’s hard to justify another set of braces, another check for null, another for i = 0;. And there you are. Old world: C. New world: not C.


The above is a small selection of things I want from a ‘modern’ language. Others might be (not in strict order):

  • Docstrings. As an Emacs user, I’m a total convert to the idea that a language should facilitate self-documenting programs. Literate CoffeeScript is a welcome move, but I miss being able to describe method parameters and return values in a defined way. The Emacs Lisp compiler complains if you don’t document a function, mentioning the params in order; this should be the norm.
  • Comprehensions are a very handy construct. I wish CoffeeScript would introduce object comprehensions, though.
  • Keyword arguments. Python can do it, Ruby is on board, and you can kind of fake it in CoffeeScript, using destructuring assignment. The king, of course, is Smalltalk, with its selectors – effectively polymorphic method signatures enhanced by keyword arguments. In Smalltalk, the selector setRed:Green:AndBlue: points to a different method than setRed: or setRed:AndGreen:. Ruby 2.0’s syntax strikes a nice balance, allowing arbitrary arguments in addition to keyworded ones.


Again, I’m not arguing what a ‘modern’ language should look like so much as observing my own prejudice; also, I’m well aware that there are horses for courses, and new(ish) languages like Go and Rust are intended for different purposes than Ruby or CoffeeScript.

I think it’s all to play for at the moment; and I think it’ll be a shame if yet another C-like language wins. My money was on Scala as a general purpose application developers’ language, but I fear it’s getting a bit astronautical. JavaScript is highly optimised, and has a (reasonably) POSIX compliant host environment – can we now consider using it for systems programming? And Ruby seems to be becoming the language of the Cloud. Perhaps we are doomed to, or blessed with, a pluralistic future.