A new programming language is useless if it doesn't solve a problem. With that in mind, I want to explore the main problem that Scotch solves.
Let's start with an analogy that expresses the basic motivation behind Scotch: Scotch aims to do for functional programming what Python has done for imperative. Or, in other words, Scotch : Haskell :: Python : C.
In terms of functionality, little of Scotch is new, although I do think the type system sets it apart from popular languages. Many significant functional programming languages already exist: Haskell, the Lisp family, the ML family, F#...so why do we need a new one?
Fortunately, Scotch has an important use case that none of these languages covers: it's an easy-to-use scripting language. Scotch is interpreted, its syntax is intuitive, its type system won't fight you, variable definitions can be redefined, and types never need to be declared: all features it shares with Python and Ruby, not other functional languages. A good developer equally familiar with Scotch and Haskell or Lisp or some other functional language will be able to throw a simple project together faster in Scotch. I'd also wager that, all things equal, this developer would be able to develop faster in Scotch than in Python, just as Python enables faster development than C.
I like to compare Scotch to Python; both are basically a bundle of things that have been done before, but both emphasize readability and developer productivity as two major selling points. Python achieves better readability in part by using simple, intuitive syntax. I would say that Scotch goes even farther in this direction because its syntax is almost identical to the most common, understandable notation in existence: math.
Take this example of function definition. In Python:
def area(length, width):
return length * width
area :: (Int a) => a -> a -> a
area length width = length * width
area(length, width) = length * width
And in math:
A(l, w) = lw
To avoid identifier ambiguity, the Scotch version is not quite the same as math, but I'd say it's close enough. Comparing the first three, the third is more concise; to anyone with a basic math background, it is also more intuitive.
Computer programs express mathematics. Historically, programming languages have contorted mathematical notation to do things we wanted to do. With Scotch, the program looks like the math that it expresses. I believe that scientists, mathematicians, or anyone who uses math in their daily lives (that's everyone) will be able to read and understand a Scotch program - instead of learning a new "language," they simply have to learn how to apply a language with which they're already familiar.
I didn't develop Scotch to be popular; I invented it to scratch my own itch, creating a kind of hybrid of two of my favorite languages, Haskell and Python. At the moment, I've written more Scotch than anyone else on Earth (and I imagine it will stay that way for some time). The verdict: I've found developing the Scotch standard library to be a refreshingly painless experience compared to other languages I've worked in.