This is the difference between a LLM and an expert. An LLM spews out a “propaganda” from the web.

### what are the unique properties of a Haskell program

1. **Statically Typed**: Haskell has a strong, static type system that ensures type safety at compile time.

2. **Purely Functional**: Haskell programs are expressions, and functions have no side effects. This leads to code that's easy to reason about, test, and debug.

3. **Lazy Evaluation**: Haskell uses lazy evaluation, meaning it only evaluates expressions when their results are needed. This can lead to more efficient programs and allows for elegant solutions like infinite data structures.

4. **Higher-Order Functions**: Functions in Haskell are first-class citizens, meaning they can be passed as arguments, returned as results, and stored in data structures.

5. **Type Classes**: Haskell's type classes (similar to interfaces in other languages) enable ad-hoc polymorphism, allowing related types to be treated uniformly.

6. **Module System**: Haskell has a rich module system that supports abstract data types, hiding implementation details, and organizing code into reusable components.

7. **Concurrency and Parallelism**: Haskell provides lightweight threads and a high-level concurrency abstraction called Software Transactional Memory (STM), along with support for parallel programming using the Glasgow Haskell Compiler (GHC).

8. **Rich Ecosystem**: Haskell has a vibrant community and a large ecosystem of libraries (via Hackage) for various domains, making it practical for real-world applications.

###

Here is what an expert answer could be:

  1. Well-typed state-machine: A pure expression which main produce, when desugared and turned into the GHC’s inner representation (which technically corresponds to the System F Omega) represents a declaration (declarative definition) of a state-machine to be executed by runtime.

    This declarative definition (of a state machine) has the same properties as any mathematical or logical expressions and, in principle, can be “executed” with a paper and pencil using only the well-understood Substitution Model of evaluation.

    This fact implies that at the source code level every Haskell program is a declarative mathematical model (within a given language semantics) of some aspects of the problem domain being captured and formally defined using Haskell pure expressions.

    This property (of being an executable form of logic) is unique among all programming languages in existence.

  2. All the “effects”, including “unsafe” are defined declaratively and within an instance of a particular Monad: Haskell programs are as pure as math or logic (it is a logic). Everything is defined declaratively as to be eventually performed by an “impure runtime”.

    Every “imperative” aspect of a program is described using just a function composition (which is just nesting of expressions) within (behind an abstraction barrier of) a particular instance of a Monad type-class (which generalizes such composition).

    One more time: everything at the Intermediate Representation (IR) level is just nesting of pure expressions, including “logical” declarations of how to eventually perform I/O and to scrutinize the values (which never cannot be actually seen) using pattern-matching expressions.

    All the “effects” can be defined within some instance of a Monad and therefore eventually executed by the runtime. Any Haskell program contains declarative descriptions of what has to be done and just this. Thus any Haskell program is still (technically) a form of logic.

  3. An executable form of logic: This is not just an abstract CS theoretical bullshit. Everything compiles and runs fast.

    A Haskell program is a declarative mathematical model of whatever it is, even if it describes I/O actions (to be eventually performed) and what not.

    As a consequence of everything being a description of what has to be done, no value can be actually “seen” in principle, they simply aren’t out there.

    Just like in mathematics, we talk about this or that well-defined property of particular kinds of values (captured and defined as types and type-classes) and using pure expressions to define what has to be done with such values (including conditionals).

  4. Minimally Extended and Augmented Simple Typed Lambda Calculus: This is what the System F Omega is, and the GHC’s Intermediate Representation (IR) just extends it with a couple of additional terms (clauses of a sum-type).

    So, your Haskell program is nested “instructions” (logical expressions) for this Universal Abstract Machine (which an interpreter of all this is).