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