The general rule of thumb I’d give is that a performance aware but not micro-optimized Haskell program will typically run in about 2x to 5x the time of a comparable C program, and will take somewhere between 2x and 10x as much memory. For a naive Haskell program the range is much bigger- maybe 2x to 10x as much time and 10x to 1000x as much memory (it’s easy to do a lot of allocations in Haskell).
For extremely optimized Haskell you can get close to the speed of C, but there’s still a garbage collector.
There are also certain classes of problem where a naive Haskell implementation can beat other languages by mile, including C, if you use the same implementation in both languages. Laziness can be really great sometimes. This didn’t happen much in practice though because the kind of code that’s really efficient with lazy evaluation is very obviously not in a strict language so people don’t usually write code that way.
In the end I’d say Haskell is a good choice for performance sensitive but not performance critical program. In a larger Haskell application if you have a performance critical bit you can usually write Haskell code that will be fast enough if you know what your doing. For something stand alone that needs to be as fast as possible, or the most critically performance sensitive parts of a bigger application, I’d consider using C or C++.
To rephrase using my experience: "performance aware" Haskell is about as "fast" as Go, but needs more memory, and both are slower than the same Java code - but both are way more fun to write ;). Optimising Go is easier for most people though, in Haskell you _really_ need to know Haskell internals (how to read core and write unboxed code) and understand laziness.
The goal of this implementation is not to be fast, but to be clear.
I am doing some inefficient things (like two pass encoding) on purpose to keep things simple and clear. So using this particular piece of code to judge a language's performance potential is not really the way to go here.
If the Haskell implementation is 3x slower than C/C++/Rust implementation, it would be acceptable.
If it's 30x slower, I would rather choose C/C++/Rust even the implementation won't be simple.
If it is even possible to be 3x faster than C/C++/Rust, then why not the mainstream programmers adopt Haskell everywhere?