Enabling assignments on tuples with let expressions (#107)

* Enabling assignments on tuples with let expressions

* Addressing comments

rust-semantics/execution/let.md

@@ -48,6 +48,26 @@ module RUST-LET
         <values> Values:Map => Values[NextId <- V] </values>
     requires notBool mayBeDefaultTypedInt(V)
 
+    // Handling tuple assignments 
+    rule
+        let (Variable:PatternNoTopAlt | .PatternNoTopAlts , RemainingToAssign:Patterns):TuplePattern 
+            = ptrValue(_,tuple(Val:Value, ValList:ValueList)) ; 
+        =>
+            let Variable = ptrValue(null, Val); 
+            ~> let (RemainingToAssign:Patterns:TuplePatternItems):TuplePattern 
+                = ptrValue(null, tuple(ValList));
+            
+
+    rule
+        let (.Patterns):TuplePattern = ptrValue(_,tuple(.ValueList)); 
+            => .K
+    
+    // Handles the case where the tuple pattern on the let expression has an extra comma, removing it
+    rule
+        let (Ps:Patterns,):TuplePattern = V:PtrValue; 
+            => let (Ps):TuplePattern = V;
+
+
 endmodule
 
 ```

tests/execution/let-expression.1.run

@@ -0,0 +1,4 @@
+new Let;
+call Let.let_final;
+return_value;
+check_eq 100_u64

tests/execution/let-expression.2.run

@@ -0,0 +1,4 @@
+new Let;
+call Let.let_mut;
+return_value;
+check_eq 100_u64

tests/execution/let-expression.3.run

@@ -0,0 +1,4 @@
+new Let;
+call Let.let_tuple;
+return_value;
+check_eq 100_u64

tests/execution/let-mut-expression.rs → tests/execution/let-expression.rs

@@ -4,17 +4,27 @@
 use multiversx_sc::imports::*;
 
 #[multiversx_sc::contract]
-pub trait LetMut {
+pub trait Let {
     #[init]
     fn init(&self) {
     }
 
     #[upgrade]
     fn upgrade(&self) {}
 
+    fn let_final(&self) -> u64 {
+        let x = 100_u64;
+        x
+    }
+
     fn let_mut(&self) -> u64 {
         let mut x = 99_u64;
         x = 100_u64;
         x
     }
+
+    fn let_tuple(&self) -> u64 {
+        let (x, y, z, w,) = (100_u64, 99_u64, 98_u64, 97_u64);
+        x
+    }
 }