seltzer v0.0.4

Seltzer

Seltzer is a programming language that provides less verbose syntax for JavaScript, while preserving JavaScript's semantics. Its core introduces absolutely no new functionality or changes in semantics, providing an exact one-to-one mapping to JavaScript.

Syntax

Variables

In Seltzer, variables can first be declared using the := operator. For instance:

x := 1

This is equivalent to, in JavaScript:

var x = 1;

Any further assignment modifying the variable x can be done using the = operator:

x = x + 1

Literals

Seltzer supports all the standard literals JavaScript does — numbers, strings, arrays and objects — with the same syntax JavaScript supplies.

aNumber = -1.2e-32
aString = "hello"
anArray = [1, 2, "hello"]
anObject = {
    here: "are",
    "some values": 1
}

Seltzer additionally supports multiline strings:

aMultilineString = """Hello, I can span
multiple lines!"""

Operators

Seltzer uses wordy operators instead of symbolic ones for logical operators, such as and, or and not.

Comments

Single line comments are written using #.

# This line will print "This is a string" to the console
console.log("This is a string")

Multi-line comments are written using triple quotes.

"""This is a multi-line comment
indicating that the following code
will print "This is a string" to
the console"""
console.log("This is a string")

Block Statements

Seltzer has the simple control flow statements if, switch, while and for.

if x > 2
    console.log(x + " is bigger than 2!")
elif x > 1
    console.log(x + " is bigger than 1!")
else
    console.log(x + " is smaller than 1!")
end

Switch statements work as follows:

switch x
case 1
    console.log("x is 1")
    break
case 2
    console.log("x is 2")
    break
default
    console.log("x is something else")
    break
end

While loops can be used like so:

while x > 2
    console.log(x + " is still bigger than 2!")
    x -= 1
end

... and C-style for loops are used like so:

for i := 0, i < 2, i += 1
    console.log(i)
end

The try...catch...finally series of statements are also familiar:

try
    # something
catch e
    # oh no, an exception!
finally
    # do some cleanup
end

Functions

Declaring functions is done with the def keyword, for instance:

add = def (a, b)
    return a + b
end

We can declare anonymous functions as function parameters as well:

product = def (xs)
    return xs.reduce(def (acc, x)
        return acc * x
    end, 1)
end

Objects

Seltzer provides some shortcuts for object syntax — for instance, :: is shorthand for .prototype:

Cat = def (name)
    this.name = name
end

Cat::speak = def (what)
    console.log(this.name + " the cat says: " + what)
end

alfonso = new Cat("alfonso")
alfonso.speak("meow")

Extensions

Seltzer also proposes a variety of extensions. These are not part of the core language, merely pieces of syntactic sugar that are derived from the core features. As such, they are not enabled by default, but can be used when supplying the applicable -X=ExtensionName flag to the compiler.

Default Arguments -X=DefaultArguments

Adds support for default arguments in function parameters.

foo = def (x=1)
    # do something with x
end

Splats -X=Splats

Adds support for variable argument lists, as well as destructuring assignments into lists.

foo = def (x, y, ys..., z)
    # do something in here
end

Negative Indexing -X=NegativeIndexing

Allow negative indexing on arrays to wrap around the list.

xs = [1, 2, 3]
xs[-1] # this is 3

This will incur extra branching for every access to an array via a numerical index, as the code will be transformed into:

xs[i < 0 ? xs.length - i : i]

Destructuring Assignment -X=DestructuringAssignment

Unpack lists into individual variables during assignment, if applicable.

[a, b, c] = [1, 2, 3] # a=1, b=2, c=3

If -X=Splats is enabled, items can also be destructured via splats:

[a, bs..., c] = [1, 2, 3, 4, 5] # a=1, bs=[2, 3, 4], c=5

Array Slices -X=ArraySlices

Python-style array slicing.

[1, 2, 3, 4, 5][5:2:-1] # this is [5, 4]

Choose Statement -X=ChooseStatement

An alternative construct for the switch statement.

choose x
when 1
    console.log("x is 1")
when 2, 3
    console.log("x is 2 or 3")
else
    console.log("what is x?")
end

This safeguards against fall-through cases.

Enhanced For -X=EnhancedFor

Provides an alternative syntax for for loops:

for x : xs
    # do for loop things in here
end

This exhibits the following properties:

• for loops will first check for the existence of an __iterator__ function attached to the object — if one exists, the iterator will be obtained from the object and the .next() method will be invoked on it repeatedly until StopIteration is raised (this is JavaScript 1.7's behavior). This will incur additional branching.
• With standard JavaScript arrays, this loops through each entry of the array by incrementing the index over the length of the array.
• With -X=DestructuringAssignment support, it is possible to do for [x, y] : xs (and with -X=Splats support, for [x, y, ys..., z] : xs.)

Range Literals -X=RangeLiterals

Range literals provide a way to generate a sequential list of numbers.

for i : 1 .. 10
    console.log(i)
end

This will print the numbers 1 through 10. It is also possible to specify a step.

for i : 2,4 .. 10
    console.log(i)
end

This will print the numbers 2, 4, 6, 8 and 10. Ranges are inclusive. Both the beginning and end numbers will be included in the range. If the next step will be a number exceeding the maximum of the range, it will not be included.

Descending ranges are also supported.

for i : 10,9 .. 1
    console.log(i)
end

This will print the numbers 10 through 1 in descending order.

However, be careful with floating point ranges, as precision loss may result in unexpected results.

Generators -X=Generators

Generators can transform functions into state machines with pausable execution.

makeCounter = def (n)
    while true
        n += 1
        yield n
    end
end

The generator can then be invoked like so:

countFromOne = makeCounter(1)
countFromOne.next() # this yields 2
countFromOne.next() # this yields 3

Comprehensions -X=Comprehensions

Comprehensions provide a succint syntax for populating arrays.

[x + 1 for x : [1, 2, 3, 4, 5] if x > 2]

Iterator comprehensions are also possible:

(x + 1 for x : [1, 2, 3, 4, 5] if x > 2)

Function Decorators -X=FunctionDecorators

Python-style function decorators.

logBeforeCall = def (f)
    return def ()
        console.log("calling some function")
        f.apply(this, arguments)
    end
end

@logBeforeCall
foo = def ()
    console.log("calling foo")
end

foo() # this logs "calling some function", then "calling foo"