use std::collections::HashMap;
use m2_syn::visit::Visit;
use m2_syn::{
Array, BinaryExpression, BinaryOperator, Component, Expr, ForLoop, IfStatement, IntegerLiteral,
List, LoopBody, ParenthesizedExpression, ParseError, Punctuated, ReturnStatement, Sequence,
SourceId, StringLiteral, Symbol, WhileLoop, parse_file,
};
#[derive(Debug, Clone, PartialEq, Eq)]
enum TypeRange<T, Q> {
Known(Vec<T>),
Deferred(Q),
}
#[derive(Debug, Clone, PartialEq, Eq)]
struct Fact<T, V, Q> {
types: TypeRange<T, Q>,
value: Option<V>,
}
#[derive(Debug, Clone, Copy)]
enum CollectionKind {
Array,
List,
Sequence,
}
#[derive(Debug, Clone, Copy)]
enum ControlKind {
If,
For,
While,
Return,
}
trait InferenceContext {
type Type: Clone;
type Value: Clone;
type Query: Clone;
fn integer(&self, literal: &IntegerLiteral) -> FactOf<Self>;
fn string(&self, literal: &StringLiteral) -> FactOf<Self>;
fn symbol(&self, symbol: &Symbol) -> FactOf<Self>;
fn binary(
&self,
node: &BinaryExpression,
left: FactOf<Self>,
right: FactOf<Self>,
) -> FactOf<Self>;
fn collection(&self, kind: CollectionKind, elements: Vec<FactOf<Self>>) -> FactOf<Self>;
fn control(&self, kind: ControlKind, neighbours: Vec<FactOf<Self>>) -> FactOf<Self>;
}
type FactOf<C> = Fact<
<C as InferenceContext>::Type,
<C as InferenceContext>::Value,
<C as InferenceContext>::Query,
>;
struct TypeChecker<'context, C: InferenceContext> {
context: &'context C,
results: Vec<FactOf<C>>,
}
impl<C: InferenceContext> TypeChecker<'_, C> {
fn infer(&mut self, expression: &Expr) -> FactOf<C> {
let old_len = self.results.len();
self.visit_expr(expression);
assert_eq!(self.results.len(), old_len + 1);
self.results.pop().expect("expression produced one fact")
}
fn components(&mut self, components: &Punctuated<Component>) -> Vec<FactOf<C>> {
components
.iter()
.filter_map(|component| match component {
Component::Expr(expression) => Some(self.infer(expression)),
Component::EmptyComponent(_) => None,
})
.collect()
}
fn loop_body(&mut self, body: &LoopBody) -> Vec<FactOf<C>> {
body.listed_value
.iter()
.chain(&body.ignored_value)
.map(|expression| self.infer(expression))
.collect()
}
}
impl<'ast, C: InferenceContext> Visit<'ast> for TypeChecker<'_, C> {
fn visit_integer_literal(&mut self, literal: &'ast IntegerLiteral) {
self.results.push(self.context.integer(literal));
}
fn visit_string_literal(&mut self, literal: &'ast StringLiteral) {
self.results.push(self.context.string(literal));
}
fn visit_symbol(&mut self, symbol: &'ast Symbol) {
self.results.push(self.context.symbol(symbol));
}
fn visit_binary_expression(&mut self, expression: &'ast BinaryExpression) {
let left = self.infer(&expression.left);
let right = self.infer(&expression.right);
self.results
.push(self.context.binary(expression, left, right));
}
fn visit_parenthesized_expression(&mut self, expression: &'ast ParenthesizedExpression) {
let fact = expression.value.as_deref().map(|value| self.infer(value));
self.results.push(fact.unwrap_or_else(|| {
self.context
.collection(CollectionKind::Sequence, Vec::new())
}));
}
fn visit_array(&mut self, array: &'ast Array) {
let elements = self.components(&array.elements);
self.results
.push(self.context.collection(CollectionKind::Array, elements));
}
fn visit_list(&mut self, list: &'ast List) {
let elements = self.components(&list.elements);
self.results
.push(self.context.collection(CollectionKind::List, elements));
}
fn visit_sequence(&mut self, sequence: &'ast Sequence) {
let elements = self.components(&sequence.elements);
self.results
.push(self.context.collection(CollectionKind::Sequence, elements));
}
fn visit_if_statement(&mut self, statement: &'ast IfStatement) {
let mut neighbours = vec![
self.infer(&statement.condition),
self.infer(&statement.then_clause.value),
];
if let Some(clause) = &statement.else_clause {
neighbours.push(self.infer(&clause.value));
}
self.results
.push(self.context.control(ControlKind::If, neighbours));
}
fn visit_for_loop(&mut self, statement: &'ast ForLoop) {
let mut neighbours = Vec::new();
if let Some(range) = &statement.range {
neighbours.extend(
range
.iterated_collection
.iter()
.chain(&range.range_start)
.chain(&range.range_end)
.map(|expression| self.infer(expression)),
);
}
neighbours.extend(statement.filter.iter().map(|value| self.infer(value)));
neighbours.extend(self.loop_body(&statement.body));
self.results
.push(self.context.control(ControlKind::For, neighbours));
}
fn visit_while_loop(&mut self, statement: &'ast WhileLoop) {
let mut neighbours = vec![self.infer(&statement.condition)];
neighbours.extend(self.loop_body(&statement.body));
self.results
.push(self.context.control(ControlKind::While, neighbours));
}
fn visit_return_statement(&mut self, statement: &'ast ReturnStatement) {
let neighbours = statement
.value
.iter()
.map(|value| self.infer(value))
.collect();
self.results
.push(self.context.control(ControlKind::Return, neighbours));
}
}
#[derive(Debug, Clone, PartialEq, Eq)]
enum DemoType {
Integer,
Number,
String,
Array,
List,
Sequence,
Thing,
}
#[derive(Debug, Clone, PartialEq, Eq)]
enum DemoValue {
Integer(i64),
}
type DemoFact = Fact<DemoType, DemoValue, String>;
struct DemoRegistry {
symbols: HashMap<String, DemoFact>,
}
impl DemoRegistry {
fn known(types: Vec<DemoType>, value: Option<DemoValue>) -> DemoFact {
Fact {
types: TypeRange::Known(types),
value,
}
}
fn deferred(query: impl Into<String>) -> DemoFact {
Fact {
types: TypeRange::Deferred(query.into()),
value: None,
}
}
}
impl InferenceContext for DemoRegistry {
type Type = DemoType;
type Value = DemoValue;
type Query = String;
fn integer(&self, literal: &IntegerLiteral) -> DemoFact {
Self::known(
vec![DemoType::Integer, DemoType::Number, DemoType::Thing],
literal.text.parse().ok().map(DemoValue::Integer),
)
}
fn string(&self, _literal: &StringLiteral) -> DemoFact {
Self::known(vec![DemoType::String, DemoType::Thing], None)
}
fn symbol(&self, symbol: &Symbol) -> DemoFact {
self.symbols
.get(&symbol.text)
.cloned()
.unwrap_or_else(|| Self::deferred(format!("symbol `{}`", symbol.text)))
}
fn binary(&self, node: &BinaryExpression, left: DemoFact, right: DemoFact) -> DemoFact {
match (&node.operator, left.value, right.value) {
(
BinaryOperator::Add(_),
Some(DemoValue::Integer(left)),
Some(DemoValue::Integer(right)),
) => Self::known(
vec![DemoType::Integer, DemoType::Number, DemoType::Thing],
Some(DemoValue::Integer(left + right)),
),
_ => Self::deferred("installed binary signature"),
}
}
fn collection(&self, kind: CollectionKind, _elements: Vec<DemoFact>) -> DemoFact {
let ty = match kind {
CollectionKind::Array => DemoType::Array,
CollectionKind::List => DemoType::List,
CollectionKind::Sequence => DemoType::Sequence,
};
Self::known(vec![ty, DemoType::Thing], None)
}
fn control(&self, kind: ControlKind, _neighbours: Vec<DemoFact>) -> DemoFact {
Self::deferred(format!("{kind:?} typing rule"))
}
}
fn infer(source: &str, context: &DemoRegistry) -> Result<DemoFact, ParseError> {
let file = parse_file(source, SourceId(1))?;
let expression = match &file.elements[0] {
m2_syn::AnyCell::ExpressionCell(cell) => cell.value.as_ref(),
_ => panic!("expected an expression cell"),
};
Ok(TypeChecker {
context,
results: Vec::new(),
}
.infer(expression))
}
fn main() -> Result<(), ParseError> {
let context = DemoRegistry {
symbols: HashMap::from([(
"answer".into(),
DemoRegistry::known(
vec![DemoType::Integer, DemoType::Number, DemoType::Thing],
Some(DemoValue::Integer(40)),
),
)]),
};
let known = infer("(answer + 2)", &context)?;
let deferred = infer("missing + 2", &context)?;
let collection = infer("{answer, missing}", &context)?;
println!("known: {known:?}");
println!("deferred: {deferred:?}");
println!("collection: {collection:?}");
Ok(())
}