Super-simple visitor doing something

This commit is contained in:
greg 2019-07-29 20:01:51 -07:00
parent 0903277b69
commit c3c515284d

View File

@ -1,13 +1,48 @@
use crate::ast::ExpressionKind;
use std::rc::Rc;
use crate::builtin::{BinOp, PrefixOp};
use crate::ast::{Expression, ExpressionKind};
pub trait ExpressionKindVisitor<T> {
fn nat_literal(&mut self, n: u64) -> T;
fn nat_literal(&mut self, n: &u64) -> T;
fn string_literal(&mut self, s: Rc<String>) -> T;
fn binexp(&mut self, op: &BinOp, lhs: &Expression, rhs: &Expression) -> T;
}
pub fn dispatch<T>(input: &mut ExpressionKind, visitor: &mut dyn ExpressionKindVisitor<T>) -> T {
pub fn dispatch<T>(input: &ExpressionKind, visitor: &mut dyn ExpressionKindVisitor<T>) -> T {
use ExpressionKind::*;
match input {
NatLiteral(n) => visitor.nat_literal(*n),
NatLiteral(n) => visitor.nat_literal(n),
StringLiteral(s) => visitor.string_literal(s.clone()),
BinExp(op, box lhs, box rhs) => visitor.binexp(op, lhs.node(), rhs.node()),
_ => panic!()
}
}
struct NumberSummer;
impl ExpressionKindVisitor<u64> for NumberSummer {
fn nat_literal(&mut self, n: &u64) -> u64 {
n.clone()
}
fn string_literal(&mut self, s: Rc<String>) -> u64 {
0
}
fn binexp(&mut self, op: &BinOp, lhs: &Expression, rhs: &Expression) -> u64 {
let lhs = dispatch(&lhs.kind, self);
let rhs = dispatch(&rhs.kind, self);
lhs + rhs
}
}
#[test]
fn yolo_swagg() {
use super::*;
let mut t = NumberSummer;
let x = ExpressionKind::NatLiteral(4);
let result = dispatch(&x, &mut t);
assert_eq!(result, 4);
}