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When comparing PureScript vs ATS, the Slant community recommends PureScript for most people. In the question“What are the best (productivity-enhancing, well-designed, and concise, rather than just popular or time-tested) programming languages?” PureScript is ranked 45th while ATS is ranked 49th. The most important reason people chose PureScript is:
Has Typeclasses and RankNTypes
Specs
Question Ranking
Pros
Pro Higher kinded types
Has Typeclasses and RankNTypes
Pro High performance FFI code
The Eff monad, which is used for FFI code, optimizes out calls to bind, and supports tail call optimization, resulting in clean, efficient Javascript. The psc compiler also specifically recognizes the ST monad, and transforms scoped variables into mutable Javascript variables, for even more efficient code.
Pro Type safety
Compiling should be your first unit test. A tight type system (static and hopefully strong) will catch many logic errors that are often difficult to spot through debugging. In languages like PureScript, if it compiles, it often runs properly.
Pro Pure functional language
You cannot have side effects, unless a function is explicitly defined as so.
Pro Modules can be compiled to CommonJS
Modules compiled to CommonJS can be included with 'require', making it incredibly simple to call Purescript code from Javascript.
Pro Has row polymorphism and extensible effects
Pro FFI
FFI system is quite good and easy to use. You can import functions curried or not curried. Records and arrays use native JS objects and arrays.
Pro Thorough documentation
The Purescript website has fairly thorough documentation for all of the language's features, and the Purescript blog contains several examples of practical usage.
Pro Awesome web frameworks
Thermite (React)
Halogen (VDOM, similar to ELM)
And hit these up with Signals, Isolated/(Managed?) Components, powerful functions and FFI
Pro Built-in formal specification
ATS has a theorem-proving type system powerful enough to prove that its functions meet their specifications. This happens at compile time with no performance impact at runtime. This can be used to prove that an ATS program doesn't have bugs commonly found in C++ programs, like "this function never leaks memory" or "this program never attempts to divide by zero" or "this buffer never overflows" or to verify pointer arithmetic, etc.
Pro Free and open-source compiler
The compiler (ATS/Postiats) is GPLv3.
Pro Functional programming
The syntax is ML-like with the usual functional language features like pattern matching and tail-call optimization.
Pro High-performance systems language
ATS works as a low-level systems language. ATS programs have performance and footprint comparable to programs written in C/C++.
Pro Good module system
Similar to Modula-3. This makes ATS a viable choice even for large-scale projects.
Pro Safe concurrency
ATS can prove its concurrent programs have no deadlocks or race conditions.
Cons
Con Lots of dependencies needed to get started
Purescript is written in Haskell, but meant to be used with Node.js. As a result, to get started , users must install ghc, cabal, node.js, grunt, and bower. Purescript also has its own compiler, and different semantics form Haskell, and so even after installing, there's still some overhead to getting productive with Purescript.
Con Lack of good IDE/tooling support
Con Documentation not updated
Con Ecosystem not stable
Con Restrictive FFI
Functions exported are all curried, and must be called as such from Javascript. The FFI syntax for importing Javascript functions, while slightly simpler and more readable than UHC/Fay's, means that calls to methods on objects must be wrapped to pass the object explicitly as a parameter.
Con Slow compilation
On large project, for example Halogen
Con No Windows version
But it does run on Cygwin.
