403 lines
13 KiB
Rust
403 lines
13 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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AirAggregate, AirAggregateCtx,
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};
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use crate::{
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asg::{
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graph::object::{ObjectIndexRelTo, ObjectIndexTo},
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ObjectKind,
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},
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f::Functor,
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parse::prelude::*,
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};
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#[cfg(doc)]
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use StackEdge::{Dangling, Reachable};
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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 {
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/// Ready for an expression;
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/// expression stack is empty.
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Ready(ExprStack<Dormant>),
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/// Building an expression.
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BuildingExpr(ExprStack<Active>, ObjectIndex<Expr>),
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}
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impl Display for AirExprAggregate {
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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 ParseState for AirExprAggregate {
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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 = AirAggregateCtx;
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type Super = AirAggregate;
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fn parse_token(
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self,
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tok: Self::Token,
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ctx: &mut Self::Context,
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) -> crate::parse::TransitionResult<Self::Super> {
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use super::ir::{AirBind::*, AirDoc::*, 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(es), AirExpr(ExprStart(op, span))) => {
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let oi = ctx.asg_mut().create(Expr::new(op, span));
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Transition(BuildingExpr(es.activate(), oi)).incomplete()
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}
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(BuildingExpr(es, poi), AirExpr(ExprStart(op, span))) => {
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let oi = poi.create_subexpr(ctx.asg_mut(), Expr::new(op, span));
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Transition(BuildingExpr(es.push(poi), oi)).incomplete()
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}
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(BuildingExpr(es, oi), AirExpr(ExprEnd(end))) => {
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let _ = oi.map_obj(ctx.asg_mut(), |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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let oi_root = ctx.dangling_expr_oi();
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match (es.pop(), dangling) {
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((es, Some(poi)), _) => {
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Transition(BuildingExpr(es, poi)).incomplete()
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}
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((es, None), true) => {
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Self::hold_dangling(ctx.asg_mut(), oi_root, oi)
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.transition(Ready(es.done()))
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}
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((es, None), false) => {
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Transition(Ready(es.done())).incomplete()
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}
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}
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}
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(BuildingExpr(es, oi), AirBind(BindIdent(id))) => {
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let result = ctx.defines(id).and_then(|oi_ident| {
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oi_ident.bind_definition(ctx.asg_mut(), id, oi)
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});
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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 result {
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Ok(oi_ident) => {
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Transition(BuildingExpr(es.reachable_by(oi_ident), oi))
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.incomplete()
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}
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Err(e) => Transition(BuildingExpr(es, oi)).err(e),
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}
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}
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(BuildingExpr(es, oi), AirBind(RefIdent(name))) => {
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let oi_ident = ctx.lookup_lexical_or_missing(name);
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Transition(BuildingExpr(
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es,
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oi.ref_expr(ctx.asg_mut(), oi_ident),
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))
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.incomplete()
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}
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(BuildingExpr(es, oi), AirDoc(DocIndepClause(clause))) => {
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oi.desc_short(ctx.asg_mut(), clause);
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Transition(BuildingExpr(es, oi)).incomplete()
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}
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(BuildingExpr(es, oi), AirDoc(DocText(text))) => Transition(
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BuildingExpr(es, oi),
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)
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.err(AsgError::InvalidDocContextExpr(oi.span(), text.span())),
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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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// Token may refer to a parent context.
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(st @ Ready(..), tok @ (AirBind(..) | AirDoc(..))) => {
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Transition(st).dead(tok)
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}
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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 AirExprAggregate {
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pub(super) fn new() -> Self {
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Self::Ready(ExprStack::default())
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}
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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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/// If there is no context able to handle such an expression,
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/// then an [`AsgError::DanglingExpr`] will be returned.
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fn hold_dangling(
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asg: &mut Asg,
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oi_root: Option<ObjectIndexTo<Expr>>,
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oi_expr: ObjectIndex<Expr>,
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) -> Result<(), AsgError> {
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oi_root
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.ok_or(AsgError::DanglingExpr(oi_expr.resolve(asg).span()))?
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.add_edge_to(asg, oi_expr, None);
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Ok(())
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}
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/// The [`ObjectIndex`] of the active expression being built,
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/// if any.
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///
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/// This will return the deepest active subexpression.
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pub(super) fn active_expr_oi(&self) -> Option<ObjectIndex<Expr>> {
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use AirExprAggregate::*;
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match self {
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Ready(_) => None,
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BuildingExpr(_, oi) => Some(*oi),
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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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#[cfg(test)]
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pub mod test;
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