⟵ Back 22 min · 2021-04-12

Update 2022-04-27: Since writing this post, Hare has undergone many changes, and has had its first public release. It's more than a year since I last looked at Hare, so expect this article to be full of outdated information.

Thoughts on Hare

It seems like every year there's a new wannabe-C-replacement. I do write a lot of C for hobby projects, so I'm acutely aware of C's many defects (to name a few: a hacky error handling system, no proper namespacing, no tagged unions, an absolutely miserable macro system, &c).

Some C replacements I've been interested in are Rust1, Zig, Myrddin, and Drew DeVault's new systems programming language, Hare.

Drew has been posting teaser sections in some of his blog posts for a while now, with snippets of code in his unnamed language showing the progress that has been made. Sometime ago (I'm not sure exactly when) he made the sources and website public, but asks readers to not share them with anyone.

Because of that, I'm going to ask you, dear reader, to please respect Drew's wishes and not share this post in any public space. This page is "unlisted" and won't appear on the frontpage, and I only intend to share this with those who are already aware of Hare. If you, due to IRC logs, public GitHub repositories, or cosmic rays, find this page, kindly keep it to yourself.

So. Let's see this Hare language website. Cute bunny logo, check. Beautiful Plan9-esque design, check. Big blue THIS IS PRE ALPHA warning box, check.

Hare is a statically typed programming language which compiles to machine code. It has manual memory management, no runtime, and uses the C ABI.

Manual memory management? check. C ABI? check. No runtime? Really? Even C has a runtime (crt.S). I think what Drew means is that there will be no massive Go/Java-like runtime.

Hare fits on a 3½" floppy disc. When it's done, you’ll be able to buy a floppy disc with Hare on it to support the project.

(from here)

Floppy disks, eh? Nice, but more or less useless.

Then we see this code snippet:

use io;

export fn main() void = {
        const greetings = [
                "Hello, world!",
                "¡Hola Mundo!",
                "Γειά σου Κόσμε!",
                "Привет мир!",
        for (let i = 0z; i < len(greetings); i += 1) {

Mm, ok. So we have a less ambiguous syntax than C does (fn main() void instead of void main(void)). We have a file extension of .ha. haha.ha. And we have... suffixes for number literals? I wonder what that z is in the 0z. It's probably the equivalent of C's size_t. There's not much else we can tell from this small snippet, though.


Just wait a moment.

What was that right before the fn main()? Is that an export keyword? And hey, there's a bunch use statements as well! Praise Allah! We have proper namespacing!! Even if this was the only benefit Hare provided over C it'd still make Hare worth using, in my humble opinion. No more stupid function prototypes in header files with an arcane, idiosyncratic macro syntax.

Alright, that's cool. Let's move on.

Read the installation steps to get Hare for your system, then read the tutorial. To see if Hare is available for your system, consult the supported platforms list.

That seems to imply there's a bunch of platforms where Hare isn't available. Well, we can't expect a new language to support every platform right from the beginning. Let see...

Supported platforms

Hare (will) support a variety of platforms. Adding new (Unix-like) platforms and architectures is relatively straightforward.

Hare does not, and will not, support any proprietary operating systems.

I beg your pardon. I take this to mean there will be no macOS or Windows support. Look, I understand that proprietary OS's suck, but deliberately choosing not to not support them means you're not going to replace a fraction of the C code that's been written out there. Hell, a major advantage of using C in the first place is the fact that there are battle-tested compilers for every imaginable platform on earth. A platform isn't a viable platform until it has a C compiler (Drew himself notes this in a post from early 2017). Sheesh.


ArchitectureSupport status

Interesting, no arm32 or i686 yet?. What compiler backend are you using? Oh, I see, you're using QBE. It's not a bad choice. You're going to miss out on LLVM's optimisations, you're going to have to finish up that half baked aarch64 code, and you're going to have to write your own code to support other architectures, but hey, you're going to get some pretty fast compiles and a much simpler compiler design! As a bonus, you'll get to use C instead of C++!

Hopefully the improvements the Hare developers makes to QBE will be upstreamed; the project seems to be unmaintained at present.

Operating systems

Operating systemSupport status
Plan 9…Planned

So... you're going out of your way to support Haiku, an arcane and obscure OS that nobody (and by "nobody", I mean "fewer than ~30 people") seriously uses, but you're going to leave out Windows and macOS? This would be OK for any other toy language, but this is a competitor for C. Come on, not everyone who uses proprietary platforms uses them because they positively enjoy doing so; a lot of people I know use Windows or macOS because they're forced to do so. But I digress.

Hare's future research areas

Hare has a list of language features that will be explored in the future and might be added to the language:

Trying out the language

Now, I could just write a brainfuck interpreter and get away with it, but I want to write some data structures and push on the standard libraries more than that. I think I'll write a Nga implementation for RetroForth. I'll be doing a loose port of vm/nga-c/barebones.c, the minimalist C implementation of Nga.

For those who are unfamiliar with RetroForth and Nga: RetroForth is a highly portable, modernised, general-purpose FORTH scripting language, and Nga is the VM Retro is implemented on.

Fast-forward a week or so. I'd spent the last few hours of the that day figuring this out before going to bed. The next morning, I continued, running into a slew of compiler quirks and bugs, one of which I submitted a patch for. Two days later, I still hadn't finished, despite this being the kind of task which would usually take me an afternoon to complete. One reason for that would be the fact that Hare is still very, very pre-alpha -- a lot of semantical errors are handled with assert's, so instead of Variably-sized arrays stored in the stack are currently unsupported you get harec: src/eval.c:27: eval_access: Assertion 'in->access.object->otype == O_DECL' failed.. Running into one of these requires peeking into the compiler and working your way backwards through the parsing code to find out what caused the error.

Eventually, I just gave up and tried the language out in other ways. I had some fun implementing hash::crc* and unix::tty::* in the stdlib and sending patches upstream.

Some thoughts on my experience, in no particular order (a bunch of these should probably be expected from an immature language and will be outdated by the time Hare reaches v1.0.):

Confusing global syntax

The syntax for global is confusing. You have the following forms:

let foo_bar: size = 0z;
const foo_bar: size = 0z;
def FOOBAR: size = 0z;

And while it's a bit obvious what the difference between let and const is, the difference between def and const is not apparent. (I'm still not entirely sure what the difference is, but I believe def is something like #define in C.)

Lack of documentation

Important topics like function pointers, memory allocation and the standard library are not being covered by the tutorial or documentation. The tutorial also lacks depth and meaty examples.

Raw Vim tooling

The Vim script is a bit unpolished, as it doesn't recognize some keywords and doesn't add or remove indentation automatically.

Nice "default-value" syntax

In Rust, to create a struct and fill in the default values for each item you must do:

struct Foo { /* snip */ }

fn myfunc() {
        let x: Foo = Default::default();

In Hare, you simply do Foo { ... }, which is much more concise and readable.

However, this only works for primitives that already have default types -- you can't define the default type for, say, a struct like you can in Rust (by implementing Default, I think, I'm not entirely sure).

Far too loose syntax for if/else/for

A commonly-cited problem with C's syntax is the fact that the braces for loops and control-flow statements are optional, enabling a lot subtle mistakes. Instead of taking care of this problem like any sane language created in 2020 would, Hare sadly does not.

Less undefined behaviour

In Hare, most behaviour that is implementation-defined (or worse, platform-defined) in C (e.g. overflow) is defined in Hare's spec.

Good Unicode support in the standard library

Hare has builtin functions for UTF-8 processing in the encoding module, which is nice (though I haven't personally used it yet, so I'm not sure how robust it is right now). You even have functions to get properties of Unicode codepoints in the unicode module! In C you'd have to pull in a separate library like libutf or utf8proc to do such things.

Builtin len function

There are many issues with the sizeof operator in C:

Instead of reciting cryptic sizeof incantations to find the length of a statically-allocated array, you get a much nicer builtin len function:

let a = [1, 2, 3];
len(a) // => 3

let buf = alloc([], 2048);  // the memory needed to store 2046 items is
                            // allocated, but the slice itself still has
                            // zero items.

len(buf);                   // => 0

for (let i = 0z; i < 20; i += 1)
        append(buf, 0z);    // Now we increase the length of the array by
                            // adding items to it.

len(buf);                   // => 20

Checked array indexing

Hare checks indexes to slices and arrays at runtime, so the following would result in an error, not an incomprehensible segfault that has to be valgrind'd to further reveal its internal mysteries:

let foo = [0z, 1z, 2z];
return foo[28];

Of course, if you want unchecked slices for performance reasons, you can have them with the *[*]type syntax.

No uninitialized variables

A common mistake in C is to declare a variable without an initializer, and then have an if/else if statement assign the variable a value without handling all the edge cases:

size_t y;

if (a > b) {
        y = a + b;
} else if (a == b) {
        y = a * b;

// What's the value of y if a < b?
This "feature" can be used to implement rand():

        // size_t x = 4;
        size_t x;
        // The value of x is undefined now.
        return x;

Some compilers warn you of this, others don't. Hare avoids the issue by disallowing all uninitialised variables entirely:

// Invalid:
let foo;

if (bar)
        foo = 0;
        foo = 89;

// Valid:
let foo = if (bar) 0 else 89;


In Hare, as in many other languages, most statements, including if/else, match, and others are expressions that can return a value:

// No ternary operator needed!
let x = if (boo()) {
} else {

// In C, this would be something like:
size_t x = 0;
if (boo()) {
        x = baz();
} else {
        x = 89;

// Or with the ternary operator in C:
size_t x = boo() ? baz() : 89;

Nullable pointers

In C, any type that has a * following it (that is, a pointer) could point to NULL. In Hare, pointers that aren't nullable (a tagged union of that pointer type and null, I think) are guaranteed to not be NULL, and pointers that are can only be dereferenced after using a match expression to ensure that they are not. To steal an example from here:

let x = 10;
let y: *int = &x;         // Guaranteed to be non-null
let z: nullable *int = y; // May be null!

*y; // Valid
*z; // Error: main.ha:6:19: Cannot dereference nullable pointer type

match (z) {
        null => abort(),
        z: *int => *z, // Valid

No variable-length arrays

You can't have variable-length arrays. The following leads to a failed assertion:

let sz = os::stat( /* snip */ )?.sz;
let buf: [sz]u8 = [0...];

Of course, when I first ran into this I assumed it was just an unimplemented feature that would be added. Sadly, it seems like there's a chance of this feature not landing at all:

  <kiedtl> Oh, one more thing: variable-length stack-stored arrays will be
           supported, correct? (e.g. in C `int foo[len];`)
<ddevault> maybe, but not likely

Semicolons everywhere!

This is definitely a non-issue, but why are there semicolons everywhere? (It might have something to do with the fact that Hare's grammar was designed to be context-free. I'm no compiler designer, so feel free to correct me on this.2)

let monsters = [ "mengele", "eichmann", "göring", "höss" ];
for (let i = 0z; i < len(monsters); i += 1) {
        if (is_convicted(monsters[i])) {
                append(death_row, monsters[i]);
        } else {
        }; // why is this necessary?
}; // or this?

Casting slices

The unintuitive and error-prone fread shouldn't be something one misses from C, but in this case, I do:

// Initialize our array... this will most likely become more ergonomic as
// the language matures.
let buf: []u8 = alloc([], sz);
for (let i = 0z; i < sz; i += 1) append(buf, 0);

// Reading an array of bytes into an array of i32's in Hare.
// Not for children under the age of 18.
io::read(fp, buf[..])?;
let buf_i32: *[*]i32 = (buf: *[*]u8: *[*]i32);

// The same thing, in C:
fread(&buf, sizeof(int32_t), fileLen, fp);

Copying slices

The slice copy syntax, which means one doesn't have to use memcpy, is really neat:

buf[a..b] = another_buf[x..y];

Lack of range syntax

Hare doesn't have iterators, but a cleaner syntax for for (let i = 0z; i < max; i += 1) (maybe something like for (i in 0..=max)) would be neat.

Empty fn/if/for statements

The following is invalid in Hare:

fn foo() void = {

if (test) {

This isn't common, unless you're debugging and commented out the code for that statement, in which case it's rather annoying. For function definitions, you can add return; to the definition to mitigate that issue.

Labeled loops

In all the languages I know of, you can't break out of a loop from an inner loop. With Hare, you can:

:outer for (<snip>) {
        :inner for (<snip>) {
                continue :outer;

I'm not yet sure whether this is a good thing or a bad thing. Sure, you can do clever shenanigans now, but something tells me this will make the code's control flow much harder to follow.

Tagged unions for error handling

In Hare, you have monadic error handling with tagged unions and error types. Additionally, one can define their own error types if necessary.

use errors;

type myerror = void!;
type error = (myerror | error::invalid)!;

fn foo() (void | error) = {
        match (frobnicate()) {
                blah: *size => booze(*blah),
                null => return errors::invalid,
        if (barbaz() && iswhyze()?)
                return myerror;

One thing I miss is an operator/method that "unwraps" the return value, and aborts if it's an error -- it's a bit annoying to have to write a match expression when I'm trying to quickly write a test program; I'd rather save that for later when I come to cleanup whatever I wrote. I think that'll be added as the language matures, though.

Update: As of April 24, the ! operator (unwrap()) is being implemented in Hare.

Lack of generics

One flaw of Hare is blazingly obvious: the lack of generics:

Hare does not support generics, and our approach to data structures is much like C: DIY. Hare supports the following basic data structures:

That’s the complete list of aggregate type classes defined by the specification. You can build arbitrarily complex data structures out of these, but, like C, Hare puts the ball in your court. For most of your application’s day-to-day data processing needs, these types are sufficient, shunting data from A to B without much fuss. For most of your data processing, these limitations will not be your bottleneck, and simpler (but slower) data structures won’t have much of an impact on your program.

Mhm. Thank you so much. I'm going to be just so bloody thrilled when it's time to convert my eighth HashMap implementation, ripped out from three other projects of mine, from <string, i32> to <string, i8>. And this bastard of a language doesn't even leave me with a crippled search-and-replace macro system to help me with this in the smallest way.3 I could use void * pointers as in C, but hell, if I enjoyed doing that I'd just use C instead.

tl;dr Regarding generic data structures, Hare "puts the ball in your court", which is a neat euphemism for "forces you to reinvent the wheel".

No functional programming

[me whining about how Hare doesn't have a pipe operator]
<ddevault> hare is not new haskell
  <kiedtl> ddevault: I guess this isn't the place to litigate this, but
           adding an operator like that doesn't mean you have to add traits,
           houses of cards^Wtypes, and other haskell abominations :V
<ddevault> hare's design ethos is to be _simple_, kiedtl
  <kiedtl> Well, if Hare's definition of "simple" is "No functional
           programming concepts, just the bare minimum to make C palatable
           in 2021", then yeah, I guess :V
<ddevault> yes, that is hare's definition of simple
  <kiedtl> Got it
<ddevault> functional programming can never succeed as a systems programming
  <kiedtl> I'd like to prove you wrong :)
<ddevault> it obfuscates too much of what's going on from the programmer
<ddevault> no
  <kiedtl> I think it makes it clearer and more concise, but that's my
           opinion :)
  <kiedtl> Well, myrlang is a thing. Too bad it's unmaintained.
<ddevault> it makes expressing your intent clearer and more concise
  <kiedtl> Oh, I see what you mean
<ddevault> but systems programming is not about expressing your intent and
           letting the compiler figure out the how
<ddevault> systems programming is about the how
  <kiedtl> Thanks, your view is clearer now :)

That's fair, I guess (except the pipe operator thing -- it's just syntax sugar, for heaven's sake). I'm just a bit confused about why closures are a "future research area" but anonymous functions won't be added:

  <kiedtl> So, closures is a "future research area" for hare, meaning that it
           *might* be implemented in the future, ...but Hare won't have "bare"
           anonymous functions (that don't capture their environment)?
<ddevault> no, probably not

Update: Drew has clarified his view:

<ddevault> simpler to add, but with less utility
<ddevault> and having two things is more complicated than having one thing

And, for the record, I agree with him. In a language without map, reduce, and other generic high-order functions, anonymous functions don't really serve much of any purpose.

Strong typing

Unlike C, in Hare one must do a lot of explicit casting between types, making it significantly harder to slash your left thumb off while trying to dereference an int cast as a struct foo *.


In some modules in the standard library (see: hash::adler32, hash::crc32, &c) a technique called "subtyping" is used, where struct B, who's first member is a struct A, is cast as that struct A to properly conform to an interface. It's supposedly common in C (that's what I was told in #hare, anyway), though this is the first time I'm encountering it.

It's not really an issue with the language itself, but it did make quite an ugly impression on me.


Hare is still a young language, and some of my criticisms of the language will be out of date before long. But the main issue is that while Hare could've been a very promising language, like the Gemini Protocol4, it seems to have taken its goal of simplicity a bit too far.

To return from the IRC quote from earlier, yes, systems programming is about the how, but only to a certain extent! I'm sure everyone agrees with this, but everyone sets a different line. Drew DeVault says "no FP stuff or high-order functions" and sets that as the boundary; yet he allows the existence of a well-fed standard library that includes hashes and streams and, goodness, Unicode! that all hide what's going on from the programmer. That's the almost the definition of a function, a chunk of reusable code that hides from the programmer what's going on!

And, yes, everyone has different opinions. In my opinion, as someone who's too used to there being at least foldl in a language's standard library (I am a spoiled brat), FP stuff is not unsuited to a systems programming language; in Drew DeVault's, it is. Whether Hare gains widespread use all depends, in the end, on how many developers side with me and how many agree with Drew.5

Then again, none of these omissions (except for the lack of generics, maybe) really cripple the language in any way. I probably wouldn't choose it for a large project, but for small ones, Hare strikes a nice balance between simplicity and power. Who knows, for small utility programs that I know won't be running on non-Linux OS's anyway, I might just end up using this.

The real question is, does Hare have an business existing when Zig and Myrddin already exist? I don't know, I barely know either of them. I was planning to implement Nga in both of those as well and to draw a lengthy comparison between the three, but I think I'll save that for a future post.


Note: If I still exist by late 2022 (not likely), when Hare is supposed to reach v1.0, I'll be updating this post.


Yes, I know that Rust is a C++ replacement, not a C replacement. What I mean by that is that I use Rust in the same places I'd normally use C.


I mean; it should be possible to build a context-free grammar without semicolons, right (see Lua); I do sometimes wonder if programmers who enjoy this syntax also talk like that in real life;


A certain blogger in the Geminispace states:

Generics are way overrated. Like any feature, generics /can/ be the most elegant solution for some problems, but they’re needlessly complex for most applications, and they tend to be way overused (right alongside overloading in C++). They add way too much complexity to both the compiler and the resulting object code to be worth the minor advantages it provides IMO.

While I do agree with the first part (except the C++ example -- just about every C++ feature is needlessly complicated and overused!) I beg to disagree with the latter. Generics done right doesn't need to add a lot of complexity to the compiler, and shouldn't add any to the resulting binary (except, maybe, a slightly larger size). Generics are, after all, just templates for functions and all the compiler should be doing is a glorified search and replace operation to condense that template into crystallized code.


Before I get swamped with hatemail from the usual crazed Gemini fundamentalists, I promise I'll condense my criticism of Gemini into a more constructive form in a future post.


I do suspect that there will be a group of hardcore Hare users, who, like the many Rust fanatics they despise, will be completely impervious to any outside criticism. (No, that's not aimed at anyone currently using/working on Hare.)

Kiëd Llaentenn © 2019-2022 — CC BY-NC-ND 4.0