logos calculator example

src/parser.rs

@@ -0,0 +1,56 @@
+use chumsky::{prelude::{just, recursive}, recursive, select, IterParser, Parser};
+
+use crate::{ast::Expression, tokens::Token};
+
+
+#[allow(clippy::let_and_return)]
+/* ANCHOR: parser */
+pub fn parser<'src>(
+) -> impl Parser<'src, &'src [Token<'src>], Expression, chumsky::extra::Err<chumsky::error::Simple<'src, Token<'src>>>>
+{
+    recursive(
+        |p| 
+        {
+            let atom = {
+            let parenthesized = p
+                .clone()
+                .delimited_by(just(Token::ParenBegin), just(Token::ParenEnd));
+
+            let integer = select! {
+                Token::Integer(n) => Expression::Integer(n),
+            };
+
+            parenthesized.or(integer)
+        };
+
+        let unary = just(Token::Substract)
+            .repeated()
+            .foldr(atom, |_op, rhs| Expression::Negate(Box::new(rhs)));
+
+        let binary_1 = unary.clone().foldl(
+            just(Token::Multiply)
+                .or(just(Token::Divide))
+                .then(unary)
+                .repeated(),
+            |lhs, (op, rhs)| match op {
+                Token::Multiply => Expression::Multiply(Box::new(lhs), Box::new(rhs)),
+                Token::Divide => Expression::Divide(Box::new(lhs), Box::new(rhs)),
+                _ => unreachable!(),
+            },
+        );
+
+        let binary_2 = binary_1.clone().foldl(
+            just(Token::Add)
+                .or(just(Token::Substract))
+                .then(binary_1)
+                .repeated(),
+            |lhs, (op, rhs)| match op {
+                Token::Add => Expression::Add(Box::new(lhs), Box::new(rhs)),
+                Token::Substract => Expression::Substract(Box::new(lhs), Box::new(rhs)),
+                _ => unreachable!(),
+            },
+        );
+
+        binary_2
+    })
+}