✨

Fasto/DeadBindingRemoval.fs

@@ -62,13 +62,9 @@ let rec removeDeadBindingsInExp (e : TypedExp) : (bool * DBRtab * TypedExp) =
              ArrayLit (es', t, pos) )
         (* ToDO: Task 3: implement the cases of `Var`, `Index` and `Let` expressions below *)
         | Var (name, pos) ->
-            (* Task 3, Hints for the `Var` case:
-                  - 1st element of result tuple: can a variable name contain IO?
-                  - 2nd element of result tuple: you have discovered a name, hence
-                        you need to record it in a new symbol table.
-                  - 3rd element of the tuple: should be the optimised expression.
-            *)
-            failwith "Unimplemented removeDeadBindingsInExp for Var"
+            let symtab = SymTab.empty()
+            let symtab = recordUse name symtab
+            (false, symtab, Var(name, pos))
         | Plus (x, y, pos) ->
             let (xios, xuses, x') = removeDeadBindingsInExp x
             let (yios, yuses, y') = removeDeadBindingsInExp y
@@ -113,12 +109,9 @@ let rec removeDeadBindingsInExp (e : TypedExp) : (bool * DBRtab * TypedExp) =
              List.fold SymTab.combine (SymTab.empty()) uses,
              Apply (fname, args', pos))
         | Index (name, e, t, pos) ->
-            (* Task 3, `Index` case: is similar to the `Var` case, except that,
-                        additionally, you also need to recursively optimize the index
-                        expression `e` and to propagate its results (in addition
-                        to recording the use of `name`).
-            *)
-            failwith "Unimplemented removeDeadBindingsInExp for Index"
+            let (eio, symtab, e') = removeDeadBindingsInExp e
+            let symtab = recordUse name symtab
+            (eio, symtab, Index(name, e', t, pos))
 
         | Let (Dec (name, e, decpos), body, pos) ->
             (* Task 3, Hints for the `Let` case:
@@ -144,7 +137,16 @@ let rec removeDeadBindingsInExp (e : TypedExp) : (bool * DBRtab * TypedExp) =
                     Let-expression.
 
             *)
-            failwith "Unimplemented removeDeadBindingsInExp for Let"
+            let (eio, esymtab, e') = removeDeadBindingsInExp e
+            let (bodyio, bodysymtab, body') = removeDeadBindingsInExp body
+            if ((isUsed name bodysymtab) || eio) then
+                let io = eio || bodyio
+                let symtab = SymTab.combine esymtab bodysymtab
+                let exp = Let (Dec (name, e', decpos), body', pos)
+                (io, symtab, exp)
+            else
+                (bodyio, bodysymtab, body')
+
         | Iota (e, pos) ->
             let (io, uses, e') = removeDeadBindingsInExp e
             (io,