507 lines
17 KiB
Rust
507 lines
17 KiB
Rust
// ASG IR expression parsing
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//
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// Copyright (C) 2014-2023 Ryan Specialty, LLC.
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//
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// This file is part of TAME.
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program. If not, see <http://www.gnu.org/licenses/>.
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//! AIR expression parser.
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//!
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//! See the [parent module](super) for more information.
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use super::{
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super::{
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graph::object::{Expr, Object},
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Asg, AsgError, ObjectIndex,
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},
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ir::AirBindableExpr,
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};
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use crate::{
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asg::{graph::object::ObjectRelTo, Ident, ObjectKind},
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f::Functor,
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parse::prelude::*,
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};
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use std::marker::PhantomData;
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#[cfg(doc)]
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use StackEdge::{Dangling, Reachable};
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/// Parse and aggregate [`Reachable`] [`Expr`]s into the graph,
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/// with expression roots bound to their associated [`Ident`]s.
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///
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/// See [`ReachableOnly`] for more information.
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pub type AirExprAggregateReachable<O> = AirExprAggregate<O, ReachableOnly<O>>;
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/// Parse and aggregate both [`Reachable`] and [`Dangling`] [`Expr`]s into
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/// the graph.
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///
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/// See [`StoreDangling`] for more information.
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pub type AirExprAggregateStoreDangling<O> =
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AirExprAggregate<O, StoreDangling<O>>;
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/// Parse an AIR expression with binding support.
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///
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/// Expressions are composable,
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/// so this parser need only care about whether it has any active
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/// expression being parsed.
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///
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/// This parser has no dead states---it
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/// handles each of its tokens and performs error recovery on invalid
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/// state transitions.
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#[derive(Debug, PartialEq)]
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pub enum AirExprAggregate<O: ObjectKind, S: RootStrategy<O>> {
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/// Ready for an expression;
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/// expression stack is empty.
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Ready(S, ExprStack<Dormant>, PhantomData<O>),
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/// Building an expression.
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BuildingExpr(S, ExprStack<Active>, ObjectIndex<Expr>),
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}
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impl<O: ObjectKind, S: RootStrategy<O>> Display for AirExprAggregate<O, S> {
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fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
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match self {
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Self::Ready(_, es, _) => {
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write!(f, "ready for expression with {es}")
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}
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Self::BuildingExpr(_, es, _) => {
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write!(f, "building expression with {es}")
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}
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}
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}
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}
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impl<O: ObjectKind, S: RootStrategy<O>> ParseState for AirExprAggregate<O, S> {
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type Token = AirBindableExpr;
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type Object = ();
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type Error = AsgError;
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type Context = Asg;
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fn parse_token(
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self,
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tok: Self::Token,
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asg: &mut Self::Context,
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) -> crate::parse::TransitionResult<Self::Super> {
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use super::ir::{AirBind::*, AirExpr::*};
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use AirBindableExpr::*;
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use AirExprAggregate::*;
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match (self, tok) {
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(Ready(root, es, _), AirExpr(ExprStart(op, span))) => {
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let oi = asg.create(Expr::new(op, span));
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Transition(BuildingExpr(root, es.activate(), oi)).incomplete()
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}
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(BuildingExpr(root, es, poi), AirExpr(ExprStart(op, span))) => {
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let oi = poi.create_subexpr(asg, Expr::new(op, span));
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Transition(BuildingExpr(root, es.push(poi), oi)).incomplete()
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}
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(BuildingExpr(root, es, oi), AirExpr(ExprEnd(end))) => {
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let _ = oi.map_obj(asg, |expr| {
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expr.map(|span| span.merge(end).unwrap_or(span))
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});
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let dangling = es.is_dangling();
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match (es.pop(), dangling) {
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((es, Some(poi)), _) => {
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Transition(BuildingExpr(root, es, poi)).incomplete()
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}
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((es, None), true) => {
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root.hold_dangling(asg, oi).transition(Ready(
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root,
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es.done(),
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PhantomData::default(),
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))
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}
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((es, None), false) => Transition(Ready(
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root,
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es.done(),
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PhantomData::default(),
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))
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.incomplete(),
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}
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}
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(BuildingExpr(root, es, oi), AirBind(BindIdent(id))) => {
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let oi_ident = root.defines(asg, id);
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// It is important that we do not mark this expression as
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// reachable unless we successfully bind the identifier.
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match oi_ident.bind_definition(asg, id, oi) {
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Ok(_) => Transition(BuildingExpr(
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root,
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es.reachable_by(oi_ident),
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oi,
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))
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.incomplete(),
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Err(e) => Transition(BuildingExpr(root, es, oi)).err(e),
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}
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}
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(BuildingExpr(root, es, oi), AirBind(RefIdent(ident))) => {
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Transition(BuildingExpr(root, es, oi.ref_expr(asg, ident)))
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.incomplete()
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}
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(st @ Ready(..), AirExpr(ExprEnd(span))) => {
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Transition(st).err(AsgError::UnbalancedExpr(span))
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}
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// The binding may refer to a parent context.
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(st @ Ready(..), tok @ AirBind(..)) => Transition(st).dead(tok),
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}
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}
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fn is_accepting(&self, _: &Self::Context) -> bool {
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matches!(self, Self::Ready(..))
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}
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}
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impl<O: ObjectKind, S: RootStrategy<O>> AirExprAggregate<O, S> {
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pub(super) fn new_in(oi: ObjectIndex<O>) -> Self {
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Self::Ready(
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S::new_root(oi),
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ExprStack::default(),
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PhantomData::default(),
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)
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}
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}
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/// Stack of held expressions,
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/// with the root expression at the bottom of the stack.
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///
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/// Expression [`ObjectIndex`]es are pushed onto this stack when
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/// parsing a subexpression,
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/// and are popped when the subexpression terminates.
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/// The active expression is _not_ stored on this stack to avoid unnecessary
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/// indirection.
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///
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/// Despite the immutable interface,
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/// this does modify the inner [`Vec`] in-place;
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/// it does not reallocate unless its capacity has been reached.
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///
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/// Unlike other parts of the system,
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/// this is heap-allocated,
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/// but should be very cache-friendly.
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/// This reason for heap allocation is that this is explicitly
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/// _unbounded_—systems like code generators ought to be able to output
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/// expressions in a tacit style without worrying about arbitrary limits.
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/// It is worth noting that the other parts of the system using
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/// stack-allocated data structures is less about performance and more
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/// about the simplicity afforded by keeping allocators out of the picture.
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/// We'll address performance issues if they appear during profiling.
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///
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/// Another benefit of using [`Vec`] here is that Rust is able to properly
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/// optimize away `memcpy`s for it,
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/// rather than having to utilize the parser's mutable context.
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/// Further,
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/// the ASG is heap-allocated,
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/// so we're not avoiding the heap anyway.
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///
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/// The interface is modeled after [Haskell's `Stack`][haskell-stack],
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/// with a slight variation for [`Self::pop`] so that we can avoid
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/// reallocation after a stack is used up,
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/// which is frequent.
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///
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/// [haskell-stack]: https://hackage.haskell.org/package/Stack/docs/Data-Stack.html
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///
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/// The stack states [`Dormant`] and [`Active`] selectively provide
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/// different APIs to enforce certain invariants,
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/// as an alternative to re-allocating an inner [`Vec`] each time a new
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/// root expression is encountered.
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#[derive(Debug, PartialEq, Eq)]
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pub struct ExprStack<S>(Vec<ObjectIndex<Expr>>, S);
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/// Expression stack is not in use and must be empty;
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/// no ongoing expression parsing.
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#[derive(Debug, PartialEq, Eq)]
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pub struct Dormant;
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/// Expression stack is in use as part of an expression parse.
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#[derive(Debug, PartialEq, Eq)]
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pub struct Active(StackEdge);
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#[derive(Debug, PartialEq, Eq)]
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pub enum StackEdge {
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/// Root expression is yet not reachable from any other object.
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///
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/// Dangling expressions are expected to transition into
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/// [`Self::Reachable`] after being bound to an identifier.
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/// Closing a dangling expression will result in a
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/// [`AsgError::DanglingExpr`].
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///
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/// Binding a sub-expression does not bind the root of the stack,
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/// since sub-expressions cannot reference their parent;
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/// a stack is dangling until its root expression has been bound to
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/// an identifier.
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Dangling,
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/// Root expression is reachable from another object.
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///
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/// The associated [`ObjectIndex`] serves as _evidence_ of this
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/// assertion.
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Reachable(ObjectIndex<Object>),
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}
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impl Display for StackEdge {
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fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
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match self {
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Self::Dangling => write!(f, "dangling"),
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Self::Reachable(oi) => {
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write!(f, "reachable (by {oi})")
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}
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}
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}
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}
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impl ExprStack<Dormant> {
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/// Mark the stack as active,
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/// exposing its stack API for use.
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///
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/// [`ExprStack::done`] will return the stack to a dormant state.
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fn activate(self) -> ExprStack<Active> {
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let Self(stack, _) = self;
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ExprStack(stack, Active(StackEdge::Dangling))
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}
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}
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impl ExprStack<Active> {
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fn push(self, item: ObjectIndex<Expr>) -> Self {
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let Self(mut stack, s) = self;
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stack.push(item);
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Self(stack, s)
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}
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/// Attempt to remove an item from the stack,
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/// returning a new stack and the item,
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/// if any.
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///
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/// This returns a new [`Self`] even if it is empty so that it can be
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/// reused without having to reallocate.
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fn pop(self) -> (Self, Option<ObjectIndex<Expr>>) {
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let Self(mut stack, s) = self;
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let oi = stack.pop();
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(Self(stack, s), oi)
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}
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/// Whether the stack is dangling.
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fn is_dangling(&self) -> bool {
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matches!(self, Self(_, Active(StackEdge::Dangling)))
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}
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/// Mark stack as reachable if processing the root expression.
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///
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/// `ident` is admitted as evidence of reachability,
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/// both for debugging and for making it more difficult to
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/// misuse this API.
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/// If the stack is already reachable,
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/// the previous identifier takes precedence.
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///
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/// If not parsing the root expression
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/// (if the stack is non-empty),
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/// this returns `self` unchanged.
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fn reachable_by<O: ObjectKind>(self, oi: ObjectIndex<O>) -> Self {
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match self {
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Self(stack, Active(StackEdge::Dangling)) if stack.is_empty() => {
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Self(stack, Active(StackEdge::Reachable(oi.widen())))
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}
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_ => self,
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}
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}
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/// Mark the stack as dormant,
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/// hiding its stack API and ensuring that its state is properly reset
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/// for the next root expression.
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///
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/// [`ExprStack::activate`] will re-activate the stack for use.
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fn done(self) -> ExprStack<Dormant> {
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let Self(stack, _) = self;
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// TODO: error if non-empty stack (unclosed expr)
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if !stack.is_empty() {
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todo!("ExprStack::done(): error on non-empty stack")
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}
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ExprStack(stack, Dormant)
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}
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}
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impl Default for ExprStack<Dormant> {
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fn default() -> Self {
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// TODO: 16 is a generous guess that is very unlikely to be exceeded
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// in practice at the time of writing,
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// even with template expansion,
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// but let's develop an informed heuristic.
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// Note that this is very unlikely to make a difference;
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// I just don't like using numbers without data to back them up.
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Self(Vec::with_capacity(16), Dormant)
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}
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}
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impl Display for ExprStack<Dormant> {
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fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
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let Self(stack, _) = self;
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write!(f, "dormant expression stack of size {}", stack.capacity())
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}
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}
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impl Display for ExprStack<Active> {
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fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
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let Self(stack, Active(edge_st)) = self;
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write!(
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f,
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"active {edge_st} expression stack of length {} and size {}",
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stack.len(),
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stack.capacity()
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)
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}
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}
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pub use root::*;
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mod root {
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use super::*;
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use std::fmt::Debug;
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/// The rooting strategy to employ after an [`Expr`] construction.
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///
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/// The method [`Self::defines`] roots an identifier,
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/// stating that the object associated with [`Self`] is responsible
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/// for the definition associated with this identifier.
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/// An identified expression will be rooted in [`Self`] even if it is a
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/// sub-expression.
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pub trait RootStrategy<O: ObjectKind>: Debug + PartialEq {
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/// Declare `oi` as the root of all accepted [`Expr`]s produced by
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/// the parser.
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fn new_root(oi: ObjectIndex<O>) -> Self;
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/// Look up the provided identifier `id` on the [`Asg`] and indicate
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/// that its definition is associated with [`Self`]'s root.
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///
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/// This is invoked for _all_ identifiers,
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/// including sub-expressions.
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fn defines(&self, asg: &mut Asg, id: SPair) -> ObjectIndex<Ident>;
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/// Hold or reject a [`Dangling`] root [`Expr`].
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///
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/// A [`Dangling`] expression is not reachable by any other object,
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/// so this strategy must decide whether to root it in [`Self`] or
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/// reject it.
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fn hold_dangling(
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&self,
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asg: &mut Asg,
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oi_expr: ObjectIndex<Expr>,
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) -> Result<(), AsgError>;
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}
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/// Accept and root only [`Reachable`] root expressions.
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///
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/// Note that a root expresion is still [`Dangling`]
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/// (and therefore not [`Reachable`])
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/// even if one of its sub-expressions has been bound to an
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/// identifier.
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/// In that case,
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/// the sub-expression will be rooted in [`Self`],
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/// but the [`Dangling`] root expression will still be rejected.
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///
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/// This expects identifiers to be rooted in the global environment,
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/// which is the package representing the active compilation unit.
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/// This may be relaxed once identifier caching is generalized;
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/// at the time of writing it is too coupled to the graph root.
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///
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/// See [`RootStrategy`] for more information.
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#[derive(Debug, PartialEq)]
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pub struct ReachableOnly<O: ObjectKind>(ObjectIndex<O>)
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where
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O: ObjectRelTo<Ident>;
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impl<O: ObjectKind> RootStrategy<O> for ReachableOnly<O>
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where
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O: ObjectRelTo<Ident>,
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{
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fn new_root(oi: ObjectIndex<O>) -> Self {
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Self(oi)
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}
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fn defines(&self, asg: &mut Asg, id: SPair) -> ObjectIndex<Ident> {
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match self {
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Self(oi_root) => asg
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.lookup_global_or_missing(id)
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.add_edge_from(asg, *oi_root, None),
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}
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}
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fn hold_dangling(
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&self,
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asg: &mut Asg,
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oi_expr: ObjectIndex<Expr>,
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) -> Result<(), AsgError> {
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Err(AsgError::DanglingExpr(oi_expr.resolve(asg).span()))
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}
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}
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/// Accept both [`Reachable`] and [`Dangling`] expressions.
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///
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/// A [`Dangling`] expression will have the [`Expr`] rooted instead of
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/// an [`Ident`].
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///
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/// Sub-expressions can be thought of as utilizing this strategy with an
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/// implicit parent [`ObjectIndex<Expr>`](ObjectIndex).
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///
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/// Unlike [`ReachableOnly`],
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/// this does _not_ cache identifiers in the global environment.
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/// See there for more information.
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///
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/// See [`RootStrategy`] for more information.
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#[derive(Debug, PartialEq)]
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pub struct StoreDangling<O: ObjectKind>(ObjectIndex<O>)
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where
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O: ObjectRelTo<Ident> + ObjectRelTo<Expr>;
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impl<O: ObjectKind> RootStrategy<O> for StoreDangling<O>
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where
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O: ObjectRelTo<Ident> + ObjectRelTo<Expr>,
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{
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fn new_root(oi: ObjectIndex<O>) -> Self {
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Self(oi)
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}
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fn defines(&self, asg: &mut Asg, name: SPair) -> ObjectIndex<Ident> {
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// This cannot simply call [`ReachableOnly`]'s `defines` because
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// we cannot cache in the global environment.
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// This can be realized once caching is generalized;
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// see the commit that introduced this comment.
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match self {
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Self(oi_root) => oi_root.declare_local(asg, name),
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}
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}
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fn hold_dangling(
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&self,
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asg: &mut Asg,
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oi_expr: ObjectIndex<Expr>,
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) -> Result<(), AsgError> {
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let Self(oi_root) = self;
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oi_root.add_edge_to(asg, oi_expr, None);
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Ok(())
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}
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}
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}
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#[cfg(test)]
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pub mod test;
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