Cream and Sugar (CnS) is a functional programming language that compiles to JavaScript. It's meant to be simple, light, and pretty, as well as a quickly digestible introduction into functional programming.
ToC:
Without further ado, let's look at a basic example. The following is a simple factorial calculator in JavaScript.
function factorial(n) {
if (n === 0) {
return 1;
} else {
return n * factorial(n - 1);
}
}
// 7 lines, 104 charsAnd this is how you'd write that using the most equivalent structures in CnS:
factorial n =>
when
n is 0 -> 1
n isnt 0 -> n * factorial n - 1
# 4 lines, 73 charsAnd this is how you'd write that using the most concise syntax in CnS:
factorial 0 => 1
factorial n => n * factorial n - 1
# 2 lines, 51 charsBut we'll get to how that 2-line example works in a minute. More importantly, there are a couple of takeaways right off the bat including...
- Function calls in CnS do not use parentheses.
- Every structure returns a value (including conditions).
- The value returned is always the final expression executed.
Also, you'll probably notice that, CnS's when expression is a lot like JavaScript's if statement but, in lieu of an "else" case, we're explicitly requiring one of our conditions to evaluate to true. This is something that sometimes bothers classical programmers at first but it's pretty standard in a lot of functional languages and you'll get used to it. The reason we do it this way is two-fold. Firstly, it has to do with the psychology of readability. But also, this way the language can complain if something we didn't intend to happen ends up happening. Instead of ambiguously erroring at some point after hitting the else case, the when expression will throw an error if it runs and doesn't find a match to one of its conditions. This lets us catch the error right away and be able to figure out more quickly where it came
from.
Now let's talk about that 2-line version of the function:
factorial 0 => 1
factorial n => n * factorial n - 1
# 2 lines, 51 charsThis example uses a concept called pattern matching. Essentially we're defining all the various patterns a developer could use in order to call the factorial function and attaching them to different function bodies that will be executed when their associated patterns are matched.
Here's how you'd read it: "If a user calls factorial of 0, return 1. If a user calls factorial of some other value (n), return n times factorial of n minus 1."
This is called a "polymorphic function", meaning that it takes on a particular form depending on how it was called by the user. It also illustrates another important facet of CnS (and indeed all major functional languages) – that all iterations should be done via recursion.
Yep, you heard that right. CnS has no, for, while, or do loops. In CnS, you recurse. That said, there are a couple of sugary structures and tons of convenience functions you can use to help make iterations quicker. CnS just sits on top of JavaScript after all so you've got Array.map and other built-in iterative methods you can use. But for cases where you'll have to define your own iterations, let's look at a basic example that implements an iterative function on our own.
each list, fun => each list, fun, 0
each [], fun, counter => counter
each list, fun, counter =>
inc = counter + 1
fun (head list), counter
each (tail list), fun, inc
# 6 lines, 171 charsAdmittedly, this could be somewhat simplified and we'll take care of that momentarily. For now, let's look at what it's doing.
We've defined three patterns for how this function could be called. If it gets called in any other way, it'll throw an error. The patterns are:
- With two arguments of indeterminate value (
list,fun). - With three arguments where the first is an empty array (
[],fun,counter). - With three arguments of indeterminate value (
list,fun,counter).
The function will return a count of how many items it was called for.
Our intent is that the user will call the function with 2 arguments constituting an array to loop over and a function to call for each item. when this happens, we'll hit the first pattern and immediately recurse with 3 arguments where the counter is set to 0.
At this point, assuming the array is not empty, we'll hit the third pattern. We'll increment the counter, call fun on the first item in the list (called head) and the original counter, then recurse with 3 arguments again. But this time, we'll pass in just the remaining list items (called tail) as well as our incremented counter.
We'll keep hitting pattern 3 until tail returns an empty array. At that point we'll hit pattern 2 and return the counter.
When we call the each function, it'll look like this:
each [1, 2, 3], fn item, index => item + index
#=> 3Notice that you can create anonymous functions using the keyword fn. This keeps our syntax consistent. Whereas a named function would be defined using something like factorial n (or, "factorial of n"), here we are using fn item, index (or, "function of item and index").
Now let's simplify our example a little bit.
each list, fun => each list, fun, 0
each [], fun, counter => counter
each [hd|tl], fun, counter =>
fun hd, counter
each tl, fun, counter + 1
# 5 lines, 144 charsHere, we've actually simplified in two ways: first, by destructuring in order to remove two unneeded function calls and, second, by removing an unnecessary assignment line.
Protip: Use pattern matching to avoid assignment lines where possible.
Let's look at destructuring. In pattern three, we're no longer using a parameter called list. Instead, we've used a destructuring technique to determine that the argument that comes in should be an array and will be separated out into two variables: hd, which indicates the first item in the
array and tl which captures the remaining array items.
You may have noticed that defining a function in this way requires that you allow future users of your code to call the function in each of its various forms and this may not be enticing to you. For example, you may want to lock users down to calling the each function with just a list and a function. You may not want them to have access to the counter because it could easily ruin the function's logic.
Never fear. You can take care of this when you export the function (or really at any other time), by using the built-in aritize function. For example...
export aritize each, 2In this example, we're exporting the each function with an arity of 2, meaning that users who import it will only be allowed to pass it 2 arguments. If they call the function with any other number of arguments, they'll get an error.
Let's just take a quick look at a final version of this function in Cream & Sugar, vs how the same function would be implemented recursively in JavaScript.
CnS
each list, fun => each list, fun, 0
each [], fun, counter => counter
each [hd|tl], fun, counter =>
fun hd, counter
each tl, fun, counter + 1
# 5 lines, 144 charsJavaScript
function each(list, fun, counter) {
if (arguments.length === 2) {
return each(list, fun, 0);
} else {
if (!list.length) {
return counter;
} else {
const hd = list[0];
const tl = list.slice(1);
fun(hd, counter);
return each(tl, fun, counter + 1);
}
}
}
// 14 lines, 303 charsNotice that the CnS version actually does a lot more in terms of throwing errors when patterns don't match and locking down arities and whatnot. But this is effectually how you'd accomplish the same thing.
One other thing we ought to mention when talking about pattern matching is using guards. Earlier we implemented a factorial function like this:
factorial 0 => 1
factorial n => n * factorial n - 1With pattern matching we actually have lots of options and another way we could implement the same thing is by using guards. Guards essentially qualify certain aspects of a pattern that are harder to express in the pattern itself.
Consider this:
factorial n where n lt 2 => 1
factorial n => n * factorial n - 1In this version of the function, we're matching against a single argument of indeterminate value in both patterns. However, in the first pattern, we qualify that match by saying where n lt 2 (or, "where n is less than 2").
The way this function is now read would be as follows: "If a user calls factorial of some value (n) where n is less than 2, return 1. If a user calls factorial n in any other case, return n times factorial of n minus 1."
Right now you may be feeling enthusiastic about Cream & Sugar for any number of reasons, but I'm willing to bet you want to hear more about the JSX support.
Well it just so happens there's a whole website full of docs for you to check out. Enjoy:
Cream & Sugar is available through npm in its raw form, as well as with both gulp plugin, a webpack loader, and a Browserify transformer! Those are located here:
The raw language npm package contains the contents of the Cream & Sugar repository. To get it, run $ npm install cream-and-sugar. If you use -g to install it globally, you'll also get access to a global bash app.
You don't care about a lot of words here, I bet. Here's an example on how to compile a file:
import { compile } from 'cream-and-sugar';
compile('path/to/file.cream', (err, result) => {
if (err) throw err;
console.log(result);
}, {finalize: true});Notice that the file extension for a Cream & Sugar file is .cream
Running the compiler on a file is an asynchronous operation behaving like most async functions in Node.js. As a third argument, you can pass in some options. For now, the only useful option is finalize which, if set to true, will make sure that all of the CnS library bootstrapping is included in the output. If you don't set this to true, you'll get the exact compiled transpilation without any necessary lib code.
Here's how you'd compile a string instead:
import { compileCode } from 'cream-and-sugar';
compileCode('add2 x => x + 2', (err, result) => {
if (err) throw err;
console.log(result);
}, {finalize: false});Notice that compileCode behaves exactly the same as compile except it takes a string of code instead of a path to a file.
The last option you have after installing this module is to play with the REPL.
To launch it, head into the CnS package directory and run $ npm install to make sure you have all of the dev dependencies. From there, run $ gulp repl. This will start up a command line environment where you can experiment with CnS syntax.