88 lines
2.7 KiB
Rust
88 lines
2.7 KiB
Rust
// Metasyntactic variables represented on the ASG
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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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//! Metasyntactic variables on the ASG.
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//!
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//! Metasyntactic variables
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//! (sometimes called "metavariables" herein for short)
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//! have historically been a feature of the template system.
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//! The canonical metavariable is the template parameter.
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use super::{
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Ident, Object, ObjectIndex, ObjectRel, ObjectRelFrom, ObjectRelTy,
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ObjectRelatable,
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};
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use crate::{
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fmt::{DisplayWrapper, TtQuote},
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parse::{util::SPair, Token},
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span::Span,
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};
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use std::fmt::Display;
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/// Metasyntactic variable (metavariable).
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///
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/// A metavariable is a lexical construct.
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/// Its value is a lexeme that represents an [`Ident`],
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/// whose meaning depends on the context in which the metavariable is
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/// referenced.
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/// Its lexeme may be composed of multiple [`Self::Lexeme`]s,
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/// and may even be constructed dynamically based on the values of other
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/// [`Meta`]s.
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///
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/// Metavariables are identified by being bound by an [`Ident`];
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/// the symbol representing that identifier then acts as a metavariable.
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#[derive(Debug, PartialEq, Eq)]
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pub enum Meta {
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Required(Span),
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ConcatList(Span),
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Lexeme(SPair),
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}
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impl Meta {
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pub fn span(&self) -> Span {
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match self {
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Self::Required(span) | Self::ConcatList(span) => *span,
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Self::Lexeme(spair) => spair.span(),
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}
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}
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}
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impl Display for Meta {
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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::Required(_) => {
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write!(f, "metasyntactic parameter with required value")
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}
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Self::ConcatList(_) => {
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write!(f, "metasyntactic concatenation list")
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}
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Self::Lexeme(spair) => write!(f, "lexeme {}", TtQuote::wrap(spair)),
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}
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}
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}
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object_rel! {
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/// Templates may expand into nearly any context,
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/// and must therefore be able to contain just about anything.
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Meta -> {
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tree Meta,
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cross Ident,
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}
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}
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