From c9d3f7629cfdacededf2a92252e6c9de8a8b75ae Mon Sep 17 00:00:00 2001
From: David Li <li.davidm96@gmail.com>
Date: Sat, 4 Nov 2017 19:18:49 -0400
Subject: Parse unary operators

---
 src/ast.rs        |  7 +++++++
 src/taiga.lalrpop | 18 +++++++++++++++---
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/src/ast.rs b/src/ast.rs
index 2814ef9..97ed91d 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -34,6 +34,12 @@ impl<T> WithLocation<T> {
 #[derive(Debug)]
 pub struct Program(pub Box<WithLocation<Expression>>);
 
+#[derive(Debug)]
+pub enum UnaryOp {
+    Pos,
+    Neg,
+}
+
 #[derive(Debug)]
 pub enum BinOp {
     Add,
@@ -45,6 +51,7 @@ pub enum BinOp {
 
 #[derive(Debug)]
 pub enum Expression {
+    UnaryOp(UnaryOp, Box<WithLocation<Expression>>),
     BinOp(BinOp, Box<WithLocation<Expression>>, Box<WithLocation<Expression>>),
     Number(u64),
     Nil,
diff --git a/src/taiga.lalrpop b/src/taiga.lalrpop
index 0182a04..6bf750d 100644
--- a/src/taiga.lalrpop
+++ b/src/taiga.lalrpop
@@ -18,15 +18,27 @@ Expression: Box<ast::WithLocation<ast::Expression>> = {
 };
 
 ExpressionMul: Box<ast::WithLocation<ast::Expression>> = {
-    <e1:ExpressionMul> "*" <e2:ExpressionBase> => Box::new(e1.join_map(*e2, |v1, v2| {
+    <e1:ExpressionMul> "*" <e2:ExpressionSign> => 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| {
+    <e1:ExpressionMul> "/" <e2:ExpressionSign> => 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| {
+    <e1:ExpressionMul> "//" <e2:ExpressionSign> => Box::new(e1.join_map(*e2, |v1, v2| {
         ast::Expression::BinOp(ast::BinOp::FloorDiv, Box::new(v1), Box::new(v2))
     })),
+    <ExpressionSign> => <>,
+};
+
+ExpressionSign: Box<ast::WithLocation<ast::Expression>> = {
+    <l: @L> "+" <e: ExpressionBase> <r: @R> => Box::new(WithLocation::new(
+        ast::Expression::UnaryOp(ast::UnaryOp::Pos, e),
+        l, r
+    )),
+    <l: @L> "-" <e: ExpressionBase> <r: @R> => Box::new(WithLocation::new(
+        ast::Expression::UnaryOp(ast::UnaryOp::Neg, e),
+        l, r
+    )),
     <ExpressionBase> => <>,
 };
 
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