hsrs

Call Rust from Haskell with type-safe, automatically generated FFI bindings.

Annotate your Rust types and functions, run the code generator, and get idiomatic Haskell that handles memory management, serialization, and type conversions for you.

Quick start

1. Annotate your Rust code

#[hsrs::module]
mod canvas {
    #[hsrs::value_type]
    pub struct Point {
        pub x: i32,
        pub y: i32,
    }

    #[hsrs::data_type]
    pub struct Canvas {
        points: Vec<Point>,
    }

    impl Canvas {
        #[hsrs::function]
        pub fn new() -> Self { Self { points: vec![] } }

        #[hsrs::function]
        pub fn add_point(&mut self, p: Point) { self.points.push(p); }

        #[hsrs::function]
        pub fn count(&self) -> u64 { self.points.len() as u64 }
    }
}

2. Generate Haskell bindings

cargo install hsrs-codegen
hsrs-codegen src/lib.rs -o Bindings.hs

3. Use from Haskell

import Bindings

main :: IO ()
main = do
  c <- new
  addPoint c (Point 10 20)
  n <- count c
  print n  -- 1

That's it. Memory is managed automatically via ForeignPtr, and complex types like Point are serialized across the boundary with Borsh.

Setup

Rust side — add hsrs to your crate:

[lib]
crate-type = ["lib", "staticlib"]

[dependencies]
hsrs = "0.1"

Haskell side — add the hsrs runtime package:

build-depends:
    hsrs >= 0.1 && < 0.2

This pulls in Borsh serialization automatically — no extra dependencies needed.

What you can annotate

Annotation	What it does	Haskell result
#[hsrs::data_type]	Opaque struct passed by pointer	ForeignPtr newtype with automatic cleanup
#[hsrs::enumeration]	C-compatible enum (repr(u8))	Word8 newtype with pattern synonyms
#[hsrs::value_type]	Struct passed by value via Borsh	data record with Borsh deriving
#[hsrs::function]	Method exported over FFI	Type-safe Haskell wrapper
#[hsrs::module]	Groups a data type with its methods	Generates all FFI glue for the type

Result<T, E> becomes Either E T, Option<T> becomes Maybe T, Vec<T> becomes [T], and String becomes Text — all serialized transparently via Borsh.

Supported types

Rust	Haskell	Transfer
i8, i16, i32, i64	Int8, Int16, Int32, Int64	Direct (C FFI)
u8, u16, u32, u64	Word8, Word16, Word32, Word64	Direct (C FFI)
bool	CBool	Direct (C FFI)
usize / isize	Word64 / Int64	Direct (C FFI)
#[hsrs::enumeration] enum	Word8 newtype + patterns	Direct (C FFI)
#[hsrs::value_type] struct	data record	Borsh
String	Text	Borsh
Vec<T>	[T]	Borsh
Option<T>	Maybe T	Borsh
Result<T, E>	Either E T	Borsh

Platform notes

usize and isize are mapped to Word64 and Int64 respectively. This matches 64-bit platforms (x86_64, aarch64). If you target 32-bit platforms, be aware that values may be truncated.

Full example

A small VM with enums, value types, Result, and Option

Rust

#[hsrs::module]
mod quecto_vm {
    #[derive(Debug, PartialEq, Eq)]
    #[hsrs::enumeration]
    pub enum Register { Reg0, Reg1, Count }

    #[derive(Debug, PartialEq, Eq)]
    #[hsrs::value_type]
    pub struct Point { pub x: i32, pub y: i32 }

    #[derive(Debug, PartialEq, Eq)]
    #[hsrs::value_type]
    pub struct VmError { pub code: u32 }

    #[hsrs::data_type]
    pub struct QuectoVm {
        registers: [i64; Register::Count as usize],
        clock: usize,
    }

    impl QuectoVm {
        #[hsrs::function]
        pub fn new() -> Self { /* ... */ }

        #[hsrs::function]
        pub fn store(&mut self, r: Register, v: i64) { /* ... */ }

        #[hsrs::function]
        pub fn snapshot(&self) -> Point { /* ... */ }

        #[hsrs::function]
        pub fn safe_div(&mut self, a: Register, b: Register) -> Result<i64, VmError> { /* ... */ }

        #[hsrs::function]
        pub fn nonzero(&self, r: Register) -> Option<i64> { /* ... */ }
    }
}

Generated Haskell

newtype Register = Register Word8
  deriving (Eq, Show, Storable)
  deriving (BorshSize, ToBorsh, FromBorsh) via Word8

pattern Reg0 :: Register
pattern Reg0 = Register 0

data Point = Point
  { pointX :: Int32
  , pointY :: Int32
  } deriving (Generic, Eq, Show)
  deriving (BorshSize, ToBorsh, FromBorsh) via AsStruct Point

data VmError = VmError
  { vmErrorCode :: Word32
  } deriving (Generic, Eq, Show)
  deriving (BorshSize, ToBorsh, FromBorsh) via AsStruct VmError

data QuectoVmRaw
newtype QuectoVm = QuectoVm (ForeignPtr QuectoVmRaw)

new       :: IO QuectoVm
store     :: QuectoVm -> Register -> Int64 -> IO ()
snapshot  :: QuectoVm -> IO Point
safeDiv   :: QuectoVm -> Register -> Register -> IO (Either VmError Int64)
nonzero   :: QuectoVm -> Register -> IO (Maybe Int64)

License

MIT OR Apache-2.0