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use std::collections::HashMap;
use syn::punctuated::Pair;
use crate::chomp::ast;
use super::cst::{Alt, Call, Cat, Fix, Ident, ParenExpression, Term};
#[derive(Clone, Copy, Debug)]
pub enum Binding {
Variable(usize),
Parameter(usize),
Global,
}
#[derive(Debug)]
pub struct Context {
names: HashMap<String, Binding>,
vars: usize,
}
impl Context {
pub fn new<I: IntoIterator<Item = Ident>>(globals: &[Ident], params: I) -> Self {
let mut names = HashMap::new();
for global in globals {
names.insert(global.to_string(), Binding::Global);
}
for (index, param) in params.into_iter().enumerate() {
names.insert(param.to_string(), Binding::Parameter(index));
}
Self { names, vars: 0 }
}
pub fn lookup(&self, name: &Ident) -> Option<Binding> {
// we make variable binding cheaper by inserting wrong and pulling right.
match self.names.get(&name.to_string()).copied() {
Some(Binding::Variable(index)) => Some(Binding::Variable(self.vars - index - 1)),
x => x,
}
}
pub fn with_variable<F: FnOnce(&mut Self) -> R, R>(&mut self, name: &Ident, f: F) -> R {
let old = self
.names
.insert(name.to_string(), Binding::Variable(self.vars));
// we make variable binding cheaper by inserting wrong and pulling right.
// we should increment all values in names instead, but that's slow
self.vars += 1;
let res = f(self);
self.vars -= 1;
if let Some(val) = old {
self.names.insert(name.to_string(), val);
} else {
self.names.remove(&name.to_string());
}
res
}
}
pub trait Convert {
fn convert(self, context: &mut Context) -> Option<ast::Expression>;
}
impl Convert for Ident {
fn convert(self, context: &mut Context) -> Option<ast::Expression> {
let span = self.span();
match context.lookup(&self)? {
Binding::Variable(index) => Some(ast::Variable::new(self, index).into()),
Binding::Parameter(index) => Some(ast::Parameter::new(self, index).into()),
Binding::Global => Some(ast::Call::new(self, Vec::new(), Some(span)).into()),
}
}
}
impl Convert for Call {
fn convert(self, context: &mut Context) -> Option<ast::Expression> {
let span = self.span();
let args = self
.args
.into_iter()
.map(|arg| arg.convert(context))
.collect::<Option<_>>()?;
Some(ast::Call::new(self.name, args, span).into())
}
}
impl Convert for Fix {
fn convert(self, context: &mut Context) -> Option<ast::Expression> {
let span = self.span();
let expr = self.expr;
let inner = context.with_variable(&self.arg, |context| expr.convert(context))?;
Some(ast::Fix::new(self.arg, inner, span).into())
}
}
impl Convert for ParenExpression {
fn convert(self, context: &mut Context) -> Option<ast::Expression> {
self.expr.convert(context)
}
}
impl Convert for Term {
fn convert(self, context: &mut Context) -> Option<ast::Expression> {
match self {
Self::Epsilon(e) => Some(e.into()),
Self::Ident(i) => i.convert(context),
Self::Literal(l) => Some(l.into()),
Self::Call(c) => c.convert(context),
Self::Fix(f) => f.convert(context),
Self::Parens(p) => p.convert(context),
}
}
}
impl Convert for Cat {
fn convert(self, context: &mut Context) -> Option<ast::Expression> {
let mut iter = self.0.into_pairs();
let mut out = match iter.next().unwrap() {
Pair::Punctuated(t, p) => (t.convert(context)?, Some(p)),
Pair::End(t) => (t.convert(context)?, None),
};
for pair in iter {
let (fst, punct) = out;
out = match pair {
Pair::Punctuated(t, p) => (
ast::Cat::new(fst, punct, t.convert(context)?).into(),
Some(p),
),
Pair::End(t) => (ast::Cat::new(fst, punct, t.convert(context)?).into(), None),
};
}
Some(out.0)
}
}
impl Convert for Alt {
fn convert(self, context: &mut Context) -> Option<ast::Expression> {
let mut iter = self.0.into_pairs();
let mut out = match iter.next().unwrap() {
Pair::Punctuated(t, p) => (t.convert(context)?, Some(p)),
Pair::End(t) => (t.convert(context)?, None),
};
for pair in iter {
let (fst, punct) = out;
out = match pair {
Pair::Punctuated(t, p) => (
ast::Alt::new(fst, punct, t.convert(context)?).into(),
Some(p),
),
Pair::End(t) => (ast::Alt::new(fst, punct, t.convert(context)?).into(), None),
};
}
Some(out.0)
}
}
|
