From f7dbbddad1f154a5f0681bd13cf87b518bfd4d26 Mon Sep 17 00:00:00 2001
From: greg <greg.shuflin@protonmail.com>
Date: Wed, 11 Jul 2018 16:44:15 -0700
Subject: [PATCH] Let and let mut syntax

---
 schala-lang/src/eval.rs       | 12 ++++++------
 schala-lang/src/parsing.rs    | 24 ++++++++++++++++--------
 schala-lang/src/tokenizing.rs |  5 +++--
 3 files changed, 25 insertions(+), 16 deletions(-)

diff --git a/schala-lang/src/eval.rs b/schala-lang/src/eval.rs
index bfc5031..64322cf 100644
--- a/schala-lang/src/eval.rs
+++ b/schala-lang/src/eval.rs
@@ -340,8 +340,8 @@ mod eval_tests {
   #[test]
   fn test_basic_eval() {
     fresh_env!("1 + 2", "3");
-    fresh_env!("var a = 1; a = 2", "Unit");
-    fresh_env!("var a = 1; a = 2; a", "2");
+    fresh_env!("let mut a = 1; a = 2", "Unit");
+    fresh_env!("let mut a = 1; a = 2; a", "2");
     fresh_env!(r#"("a", 1 + 2)"#, r#"("a", 3)"#);
   }
 
@@ -354,18 +354,18 @@ mod eval_tests {
   #[test]
   fn scopes() {
     let scope_ok = r#"
-    const a = 20
+    let a = 20
     fn haha() {
-      const a = 10
+      let a = 10
       a
     }
     haha()
     "#;
     fresh_env!(scope_ok, "10");
     let scope_ok = r#"
-    const a = 20
+    let a = 20
     fn haha() {
-      const a = 10
+      let a = 10
       a
     }
     a
diff --git a/schala-lang/src/parsing.rs b/schala-lang/src/parsing.rs
index 75ea3ee..658bf25 100644
--- a/schala-lang/src/parsing.rs
+++ b/schala-lang/src/parsing.rs
@@ -44,8 +44,12 @@ formal_param := IDENTIFIER type_anno+
 
 /* Declaration - Variable bindings */
 
+/* OLD */
 binding_declaration: 'var' IDENTIFIER '=' expression | 'const' IDENTIFIER '=' expression
 
+/* NEW */
+binding_declaration := 'let' 'mut'? IDENTIFIER '=' expresion
+
 /* Declaration - Interface */
 
 interface_declaration := 'interface' interface_name signature_block
@@ -296,7 +300,7 @@ impl Parser {
     match self.peek() {
       Keyword(Type) => self.type_declaration().map(|decl| { Statement::Declaration(decl) }),
       Keyword(Func)=> self.func_declaration().map(|func| { Statement::Declaration(func) }),
-      Keyword(Var) | Keyword(Const) => self.binding_declaration().map(|decl| Statement::Declaration(decl)),
+      Keyword(Let) => self.binding_declaration().map(|decl| Statement::Declaration(decl)),
       Keyword(Interface) => self.interface_declaration().map(|decl| Statement::Declaration(decl)),
       Keyword(Impl) => self.impl_declaration().map(|decl| Statement::Declaration(decl)),
       _ => self.expression().map(|expr| { Statement::ExpressionStatement(expr) } ),
@@ -396,10 +400,14 @@ impl Parser {
   });
 
   parse_method!(binding_declaration(&mut self) -> ParseResult<Declaration> {
-    let constant = match self.next() {
-      Keyword(Var) => false,
-      Keyword(Const) => true,
-      _ => return ParseError::new("Expected 'var' or 'const'"),
+
+    expect!(self, Keyword(Kw::Let));
+    let constant = match self.peek() {
+      Keyword(Kw::Mut) => {
+        self.next();
+        false 
+      }
+      _ => true
     };
     let name = self.identifier()?;
     expect!(self, Operator(ref o) if **o == "=");
@@ -1178,8 +1186,8 @@ fn a(x) {
 
   #[test]
   fn parsing_bindings() {
-    parse_test!("var a = 10", AST(vec![Declaration(Binding { name: rc!(a), constant: false, expr: ex!(NatLiteral(10)) } )]));
-    parse_test!("const a = 2 + 2", AST(vec![Declaration(Binding { name: rc!(a), constant: true, expr: ex!(binexp!("+", NatLiteral(2), NatLiteral(2))) }) ]));
+    parse_test!("let mut a = 10", AST(vec![Declaration(Binding { name: rc!(a), constant: false, expr: ex!(NatLiteral(10)) } )]));
+    parse_test!("let a = 2 + 2", AST(vec![Declaration(Binding { name: rc!(a), constant: true, expr: ex!(binexp!("+", NatLiteral(2), NatLiteral(2))) }) ]));
   }
 
   #[test]
@@ -1294,7 +1302,7 @@ fn a(x) {
 
   #[test]
   fn parsing_type_annotations() {
-    parse_test!("const a = b : Int", AST(vec![
+    parse_test!("let a = b : Int", AST(vec![
       Declaration(Binding { name: rc!(a), constant: true, expr:
         Expression(val!("b"), Some(ty!("Int"))) })]));
 
diff --git a/schala-lang/src/tokenizing.rs b/schala-lang/src/tokenizing.rs
index 2b4b8fd..79badbe 100644
--- a/schala-lang/src/tokenizing.rs
+++ b/schala-lang/src/tokenizing.rs
@@ -50,7 +50,8 @@ pub enum Kw {
   Func,
   For, While,
   Match,
-  Var, Const, Let, In,
+  Const, Let, In,
+  Mut,
   Return,
   Alias, Type, SelfType, SelfIdent,
   Interface, Impl,
@@ -68,10 +69,10 @@ lazy_static! {
       "fn" => Kw::Func,
       "for" => Kw::For,
       "while" => Kw::While,
-      "var" => Kw::Var,
       "const" => Kw::Const,
       "let" => Kw::Let,
       "in" => Kw::In,
+      "mut" => Kw::Mut,
       "return" => Kw::Return,
       "alias" => Kw::Alias,
       "type" => Kw::Type,