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233 lines (212 loc) · 6.71 KB
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// SPDX-License-Identifier: MPL-2.0
// SPDX-FileCopyrightText: 2024-2025 hyperpolymath
//! Effect Handling Runtime for AffineScript
//!
//! This module implements the runtime support for algebraic effects,
//! using evidence-passing compilation (Koka-style).
//!
//! # Architecture
//!
//! ```text
//! ┌─────────────────────────────────────────────────────────────┐
//! │ Handler Stack │
//! ├─────────────────────────────────────────────────────────────┤
//! │ Handler N │ Handler N-1 │ ... │ Handler 1 │ Base │
//! └─────────────────────────────────────────────────────────────┘
//! │ │ │
//! ▼ ▼ ▼
//! ┌──────────┐ ┌──────────┐ ┌──────────┐
//! │ Evidence │ │ Evidence │ │ Evidence │
//! │ (ops) │ │ (ops) │ │ (ops) │
//! └──────────┘ └──────────┘ └──────────┘
//! ```
//!
//! # Evidence Passing
//!
//! Each effect operation receives an "evidence" parameter that contains:
//! - Pointer to the handler function for that operation
//! - Captured environment from the handler
//! - Continuation management data
#[cfg(not(feature = "std"))]
use core::ptr::NonNull;
#[cfg(feature = "std")]
use std::ptr::NonNull;
/// Evidence for an effect operation
///
/// This is passed to effectful functions and contains the handler
/// to invoke when an operation is performed.
#[repr(C)]
pub struct Evidence {
/// Pointer to the handler function
pub handler: *const (),
/// Captured environment
pub env: *mut (),
/// Parent evidence (for nested handlers)
pub parent: *mut Evidence,
/// Handler frame pointer
pub frame: *mut HandlerFrame,
}
impl Evidence {
/// Create new evidence
pub fn new(handler: *const (), env: *mut (), parent: *mut Evidence) -> Self {
Evidence {
handler,
env,
parent,
frame: core::ptr::null_mut(),
}
}
}
/// Handler frame on the stack
///
/// Tracks the state needed to resume a continuation.
#[repr(C)]
pub struct HandlerFrame {
/// Saved stack pointer
pub sp: *mut u8,
/// Saved frame pointer
pub fp: *mut u8,
/// Return address
pub ra: *const (),
/// Effect signature being handled
pub effect_id: u32,
/// Whether this is a one-shot or multi-shot handler
pub is_linear: bool,
/// Parent frame
pub parent: *mut HandlerFrame,
}
/// Continuation representation
///
/// Captures the state needed to resume execution after an effect operation.
#[repr(C)]
pub struct Continuation {
/// Saved execution state
pub frame: HandlerFrame,
/// Captured stack segment (for multi-shot)
pub stack: Option<NonNull<u8>>,
/// Stack segment size
pub stack_size: usize,
/// Whether this continuation has been used
pub used: bool,
}
/// Handler for an effect
///
/// Contains the implementation of each operation.
#[repr(C)]
pub struct Handler {
/// Operation implementations (function pointers)
pub operations: *const *const (),
/// Number of operations
pub num_ops: usize,
/// Return clause
pub return_fn: *const (),
/// Captured environment
pub env: *mut (),
}
/// Global handler stack
struct HandlerStack {
/// Top of stack
top: *mut HandlerFrame,
/// Stack of installed handlers
handlers: [*mut Handler; 64],
/// Number of installed handlers
count: usize,
}
static mut HANDLER_STACK: HandlerStack = HandlerStack {
top: core::ptr::null_mut(),
handlers: [core::ptr::null_mut(); 64],
count: 0,
};
/// Initialize the effect system
pub fn init() {
// TODO: Phase 6 implementation
// - [ ] Set up initial handler frame
// - [ ] Install default handlers for built-in effects
// - [ ] Initialize continuation pool
}
/// Install a handler
///
/// # Arguments
///
/// * `handler` - The handler to install
/// * `evidence` - Evidence to populate
///
/// # Returns
///
/// Opaque handle for uninstalling
#[no_mangle]
pub extern "C" fn install_handler(handler: *mut Handler, evidence: *mut Evidence) -> u32 {
// TODO: Phase 6 implementation
// - [ ] Push handler onto stack
// - [ ] Set up evidence
// - [ ] Return handle
0
}
/// Uninstall a handler
///
/// # Arguments
///
/// * `handle` - Handle returned by `install_handler`
#[no_mangle]
pub extern "C" fn uninstall_handler(handle: u32) {
// TODO: Phase 6 implementation
// - [ ] Pop handler from stack
// - [ ] Restore previous evidence
}
/// Perform an effect operation
///
/// # Arguments
///
/// * `evidence` - Evidence for the effect
/// * `op_index` - Index of the operation to perform
/// * `arg` - Argument to the operation
///
/// # Returns
///
/// Result of the operation
#[no_mangle]
pub extern "C" fn perform(evidence: *mut Evidence, op_index: u32, arg: *mut ()) -> *mut () {
// TODO: Phase 6 implementation
// - [ ] Look up handler in evidence
// - [ ] Create continuation
// - [ ] Call handler with continuation
core::ptr::null_mut()
}
/// Resume a continuation
///
/// # Arguments
///
/// * `k` - The continuation to resume
/// * `value` - Value to pass to the continuation
///
/// # Returns
///
/// Result of resuming
#[no_mangle]
pub extern "C" fn resume(k: *mut Continuation, value: *mut ()) -> *mut () {
// TODO: Phase 6 implementation
// - [ ] Check if continuation is linear and already used
// - [ ] Restore execution state
// - [ ] Jump to continuation point
core::ptr::null_mut()
}
/// Abort an effect (for one-shot handlers)
///
/// # Arguments
///
/// * `evidence` - Evidence for the effect
/// * `value` - Value to return
#[no_mangle]
pub extern "C" fn abort_effect(evidence: *mut Evidence, value: *mut ()) -> ! {
// TODO: Phase 6 implementation
// - [ ] Unwind to handler frame
// - [ ] Call return clause
loop {}
}
// TODO: Phase 6 implementation
// - [ ] Implement evidence passing transform in codegen
// - [ ] Implement handler frame management
// - [ ] Implement one-shot continuation optimization
// - [ ] Implement multi-shot continuation copying
// - [ ] Add effect row tracking at runtime (for debugging)
// - [ ] Implement tail-resumptive optimization