just/src/tree.rs
Casey Rodarmor b2285ce0e0
Reform Parser (#509)
Just's first parser performed both parsing, i.e the transformation of a
token stream according to the language grammar, and a number of consistency
checks and analysis passes.

This made parsing and analysis quite complex, so this diff introduces a
new, much cleaner `Parser`, and moves existing analysis into a dedicated
`Analyzer`.
2019-11-07 10:55:15 -08:00

131 lines
3.0 KiB
Rust

use crate::common::*;
use std::mem;
/// Construct a `Tree` from a symbolic expression literal. This macro, and the
/// Tree type, are only used in the Parser unit tests, as a concise notation
/// representing the expected results of parsing a given string.
macro_rules! tree {
{
($($child:tt)*)
} => {
$crate::tree::Tree::List(vec![$(tree!($child),)*])
};
{
$atom:ident
} => {
$crate::tree::Tree::atom(stringify!($atom))
};
{
$atom:literal
} => {
$crate::tree::Tree::atom(format!("\"{}\"", $atom))
};
{
#
} => {
$crate::tree::Tree::atom("#")
};
{
+
} => {
$crate::tree::Tree::atom("+")
};
}
/// A `Tree` is either…
#[derive(Debug, PartialEq)]
pub(crate) enum Tree<'text> {
/// …an atom containing text, or…
Atom(Cow<'text, str>),
/// …a list containing zero or more `Tree`s.
List(Vec<Tree<'text>>),
}
impl<'text> Tree<'text> {
/// Construct an Atom from a text scalar
pub(crate) fn atom(text: impl Into<Cow<'text, str>>) -> Tree<'text> {
Tree::Atom(text.into())
}
/// Construct a List from an iterable of trees
pub(crate) fn list(children: impl IntoIterator<Item = Tree<'text>>) -> Tree<'text> {
Tree::List(children.into_iter().collect())
}
/// Convenience function to create an atom containing quoted text
pub(crate) fn string(contents: impl AsRef<str>) -> Tree<'text> {
Tree::atom(format!("\"{}\"", contents.as_ref()))
}
/// Push a child node into self, turning it into a List if it was an Atom
pub(crate) fn push(self, tree: impl Into<Tree<'text>>) -> Tree<'text> {
match self {
Tree::List(mut children) => {
children.push(tree.into());
Tree::List(children)
}
Tree::Atom(text) => Tree::List(vec![Tree::Atom(text), tree.into()]),
}
}
/// Extend a self with a tail of Trees, turning self into a List if it
/// was an Atom
pub(crate) fn extend<I, T>(self, tail: I) -> Tree<'text>
where
I: IntoIterator<Item = T>,
T: Into<Tree<'text>>,
{
// Tree::List(children.into_iter().collect())
let mut head = match self {
Tree::List(children) => children,
Tree::Atom(text) => vec![Tree::Atom(text)],
};
for child in tail {
head.push(child.into());
}
Tree::List(head)
}
/// Like `push`, but modify self in-place
pub(crate) fn push_mut(&mut self, tree: impl Into<Tree<'text>>) {
let tree = mem::replace(self, Tree::List(Vec::new())).push(tree.into());
mem::replace(self, tree);
}
}
impl Display for Tree<'_> {
fn fmt(&self, f: &mut Formatter) -> fmt::Result {
match self {
Tree::List(children) => {
write!(f, "(")?;
for (i, child) in children.iter().enumerate() {
if i > 0 {
write!(f, " ")?;
}
write!(f, "{}", child)?;
}
write!(f, ")")
}
Tree::Atom(text) => write!(f, "{}", text),
}
}
}
impl<'text, T> From<T> for Tree<'text>
where
T: Into<Cow<'text, str>>,
{
fn from(text: T) -> Tree<'text> {
Tree::Atom(text.into())
}
}