5 ms·

If Haskell is so simple, why is GHC so big? I see your claim repeated often on HN, but I think it's disingenuous.

by Volt 9y ago

mej10 9y ago
Because GHC isn't a compiler for just "Haskell -- the standardized language". It also implements a huge number of optional language extensions.
mikekchar 9y ago
Hopefully other people more knowledgeable will answer, but there are a couple things that are pretty obvious off the top of my head: - lazy evaluation - type inference - ridiculous amounts of programmer tools (it *derives* type classes for you!!!) - lots of experimental ideas that are in the compiler but that people don't really use (it's a research tool after all). The language is simple from a conceptual standpoint. Not every thing in the compiler is there simply to support expression of an idea. Quite a lot of it is there to help the programmer. I think there is something to be said for the idea of writing a similar language which has a less monolithic set of tools (although, to be fair, I have not look at the architecture of GHC at all, so maybe it is really beautiful under the hood). The point is that I don't think that you can necessarily equate the simplicity of expression with the complexity of the tools.
xrange 9y ago
Does GHC still come with a copy of GCC and Perl? Hugs is pretty small: https://www.haskell.org/hugs/ https://www.haskell.org/hugs/
tathougies 9y ago
A compiler takes one language (usually higher level) and transforms it into another (usually lower level). GHC, like C, go, or rust compilers, compiles to assembler, a very low-level and complicated language. One would expect that a system to transform a simple high level language into a complicated low level language would would grow proportional to how simple and high level the source language is. Thus, a very simple, high-level language ought to have a larger compiler than a more complicated, lower-level language. Indeed, we see this in real life. Writing a haskell compiler is a fairly big undertaking whereas a C compiler could be written in a few days. This is because C is complicated, but low-level, and Haskell is simple, but high-level. Let's not confuse the simplicity of translation with the simplicity of semantics.
- qznc 9y ago
  I believe a toy Haskell compiler could be made with comparable effort to toy C compilers. Admittedly, I cannot find people making toy Haskell compilers. What makes Haskell higher-level than C? Garbage collection does not really complicate the compiler if you just use BoehmGC. You can use a simple subset of assembly instead of the full complicated set. Toy C compilers do this, e.g. by treating x86 as a stack machine.
jlouis 9y ago
Simple languages often require complex compilers if they are to run fast. You need to do more analysis of the program structure to squeeze out performance.

If Haskell is so simple, why is GHC so big? I see your claim repeated often on HN, but I think it's disingenuous.

by Volt 9y ago

If Haskell is so simple, why is GHC so big? I see your claim repeated often on HN, but I think it's disingenuous.

Because GHC isn't a compiler for just "Haskell -- the standardized language". It also implements a huge number of optional language extensions.

mikekchar 9y ago

Hopefully other people more knowledgeable will answer, but there are a couple things that are pretty obvious off the top of my head: - lazy evaluation - type inference - ridiculous amounts of programmer tools (it *derives* type classes for you!!!) - lots of experimental ideas that are in the compiler but that people don't really use (it's a research tool after all). The language is simple from a conceptual standpoint. Not every thing in the compiler is there simply to support expression of an idea. Quite a lot of it is there to help the programmer. I think there is something to be said for the idea of writing a similar language which has a less monolithic set of tools (although, to be fair, I have not look at the architecture of GHC at all, so maybe it is really beautiful under the hood). The point is that I don't think that you can necessarily equate the simplicity of expression with the complexity of the tools.

xrange 9y ago

Does GHC still come with a copy of GCC and Perl? Hugs is pretty small: https://www.haskell.org/hugs/ https://www.haskell.org/hugs/

tathougies 9y ago

A compiler takes one language (usually higher level) and transforms it into another (usually lower level). GHC, like C, go, or rust compilers, compiles to assembler, a very low-level and complicated language. One would expect that a system to transform a simple high level language into a complicated low level language would would grow proportional to how simple and high level the source language is. Thus, a very simple, high-level language ought to have a larger compiler than a more complicated, lower-level language. Indeed, we see this in real life. Writing a haskell compiler is a fairly big undertaking whereas a C compiler could be written in a few days. This is because C is complicated, but low-level, and Haskell is simple, but high-level. Let's not confuse the simplicity of translation with the simplicity of semantics.

qznc 9y ago
I believe a toy Haskell compiler could be made with comparable effort to toy C compilers. Admittedly, I cannot find people making toy Haskell compilers. What makes Haskell higher-level than C? Garbage collection does not really complicate the compiler if you just use BoehmGC. You can use a simple subset of assembly instead of the full complicated set. Toy C compilers do this, e.g. by treating x86 as a stack machine.

jlouis 9y ago

Simple languages often require complex compilers if they are to run fast. You need to do more analysis of the program structure to squeeze out performance.