From 9f393b2eb7b3fb8f1924e80095bad3384049cc67 Mon Sep 17 00:00:00 2001
From: David Li <li.davidm96@gmail.com>
Date: Sat, 4 Nov 2017 20:15:20 -0400
Subject: Parse let expressions

---
 src/ast.rs        | 19 +++++++++++++++++++
 src/taiga.lalrpop | 19 +++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/src/ast.rs b/src/ast.rs
index 22d968e..7edf9c7 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -60,6 +60,7 @@ pub enum BinOp {
 
 #[derive(Debug)]
 pub enum Expression {
+    Let(Vec<WithLocation<VarDec>>, Box<WithLocation<Expression>>),
     UnaryOp(UnaryOp, Box<WithLocation<Expression>>),
     BinOp(BinOp, Box<WithLocation<Expression>>, Box<WithLocation<Expression>>),
     Number(u64),
@@ -67,3 +68,21 @@ pub enum Expression {
     Name(String),
     Nil,
 }
+
+#[derive(Debug)]
+pub struct VarDec {
+    name: WithLocation<String>,
+    type_: Option<String>,
+    value: Box<WithLocation<Expression>>,
+}
+
+impl VarDec {
+    pub fn new(name: WithLocation<String>, type_: Option<String>,
+               value: Box<WithLocation<Expression>>) -> VarDec {
+        VarDec {
+            name: name,
+            type_: type_,
+            value: value,
+        }
+    }
+}
diff --git a/src/taiga.lalrpop b/src/taiga.lalrpop
index be47147..851cb24 100644
--- a/src/taiga.lalrpop
+++ b/src/taiga.lalrpop
@@ -7,6 +7,19 @@ pub Program: ast::Program = {
     Expression => ast::Program(<>),
 };
 
+VarDec: Box<WithLocation<ast::VarDec>> =
+    <l: @L> "var" <name: Name> "=" <exp: Expression> <r: @R> =>
+    Box::new(WithLocation::new(ast::VarDec::new(name, None, exp), l, r));
+
+DeclarationsList: Vec<WithLocation<ast::VarDec>> = {
+    <h: DeclarationsList> <t: VarDec> => {
+        let mut h = h;
+        h.push(*t);
+        h
+    },
+    <VarDec> => vec![*<>],
+};
+
 Expression: Box<ast::WithLocation<ast::Expression>> = {
     <e1:Expression> "&&" <e2:ExpressionEq> => Box::new(e1.join_map(*e2, |v1, v2| {
         ast::Expression::BinOp(ast::BinOp::And, Box::new(v1), Box::new(v2))
@@ -87,6 +100,8 @@ ExpressionBase: Box<ast::WithLocation<ast::Expression>> = {
     String => Box::new(<>.map(|v| ast::Expression::String(v))),
     Name => Box::new(<>.map(|v| ast::Expression::Name(v))),
     Spanned<r"nil"> => Box::new(<>.map(|v| ast::Expression::Nil)),
+    <l: @L> "let" <d: DeclarationsList> "in" <e: Expression> "end" <r: @R> =>
+        Box::new(WithLocation::new(ast::Expression::Let(d, e), l, r)),
     "(" <Expression> ")" => <>,
 };
 
@@ -102,6 +117,10 @@ Spanned<T>: WithLocation<T> = {
 
 match {
     "nil",
+    "var",
+    "let",
+    "in",
+    "end",
 }
 else {
     r"[[:alpha:]_][[:alpha:]_0-9]*",
-- 
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