From ee7c269301f84bd5c7c942900aaa2d96d17d886f Mon Sep 17 00:00:00 2001
From: David Li <li.davidm96@gmail.com>
Date: Sat, 4 Nov 2017 19:06:13 -0400
Subject: Parse binary operators with precedence

---
 src/ast.rs        | 22 ++++++++++++++++++++++
 src/main.rs       |  2 +-
 src/taiga.lalrpop | 25 +++++++++++++++++++++++++
 3 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/src/ast.rs b/src/ast.rs
index 3863ce9..2814ef9 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -18,12 +18,34 @@ impl<T> WithLocation<T> {
             location: self.location,
         }
     }
+
+    pub fn join_map<U, V, F>(self, other: WithLocation<U>, f: F) -> WithLocation<V>
+        where F: FnOnce(WithLocation<T>, WithLocation<U>) -> V
+    {
+        let loc1 = self.location;
+        let loc2 = other.location;
+        WithLocation {
+            value: f(self, other),
+            location: (loc1.0, loc2.1),
+        }
+    }
 }
 
 #[derive(Debug)]
 pub struct Program(pub Box<WithLocation<Expression>>);
 
+#[derive(Debug)]
+pub enum BinOp {
+    Add,
+    Sub,
+    Mul,
+    Div,
+    FloorDiv,
+}
+
 #[derive(Debug)]
 pub enum Expression {
+    BinOp(BinOp, Box<WithLocation<Expression>>, Box<WithLocation<Expression>>),
     Number(u64),
+    Nil,
 }
diff --git a/src/main.rs b/src/main.rs
index 5b343ec..bd4659b 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -2,5 +2,5 @@ pub mod ast;
 pub mod taiga;
 
 fn main() {
-    println!("{:?}", taiga::parse_Program("5"));
+    println!("{:?}", taiga::parse_Program("(3 + 5) * 7"));
 }
diff --git a/src/taiga.lalrpop b/src/taiga.lalrpop
index 08c3cd3..0182a04 100644
--- a/src/taiga.lalrpop
+++ b/src/taiga.lalrpop
@@ -8,7 +8,32 @@ pub Program: ast::Program = {
 };
 
 Expression: Box<ast::WithLocation<ast::Expression>> = {
+    <e1:Expression> "+" <e2:ExpressionMul> => Box::new(e1.join_map(*e2, |v1, v2| {
+        ast::Expression::BinOp(ast::BinOp::Add, Box::new(v1), Box::new(v2))
+    })),
+    <e1:Expression> "-" <e2:ExpressionMul> => Box::new(e1.join_map(*e2, |v1, v2| {
+        ast::Expression::BinOp(ast::BinOp::Sub, Box::new(v1), Box::new(v2))
+    })),
+    <ExpressionMul> => <>,
+};
+
+ExpressionMul: Box<ast::WithLocation<ast::Expression>> = {
+    <e1:ExpressionMul> "*" <e2:ExpressionBase> => Box::new(e1.join_map(*e2, |v1, v2| {
+        ast::Expression::BinOp(ast::BinOp::Mul, Box::new(v1), Box::new(v2))
+    })),
+    <e1:ExpressionMul> "/" <e2:ExpressionBase> => Box::new(e1.join_map(*e2, |v1, v2| {
+        ast::Expression::BinOp(ast::BinOp::Div, Box::new(v1), Box::new(v2))
+    })),
+    <e1:ExpressionMul> "//" <e2:ExpressionBase> => Box::new(e1.join_map(*e2, |v1, v2| {
+        ast::Expression::BinOp(ast::BinOp::FloorDiv, Box::new(v1), Box::new(v2))
+    })),
+    <ExpressionBase> => <>,
+};
+
+ExpressionBase: Box<ast::WithLocation<ast::Expression>> = {
     Num => Box::new(<>.map(|v| ast::Expression::Number(v))),
+    Spanned<r"nil"> => Box::new(<>.map(|v| ast::Expression::Nil)),
+    "(" <Expression> ")" => <>,
 };
 
 Num: WithLocation<u64> = <e: Spanned<r"[0-9]+">> => e.map(|v| u64::from_str(v).unwrap());
-- 
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