Add block expressions and if expressions

If and block statements are now expressions. The last expression, if
any, is used as the return value of this expression.

Also fixed a (major) bug in the if statement generation that was causing
the wrong jump address to be generated.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

tools/genast.py

@@ -250,6 +250,24 @@ GENERATE = [
     .add_struct("List", ["lbracket: Token", "exprs: Vec<ExprP>", "rbracket: Token"])
     .add_struct(
         "Map", ["lbracket: Token", "pairs: Vec<(ExprP, ExprP)>", "rbracket: Token"]
+    )
+    .add_struct(
+        "If",
+        [
+            "if_kw: Token",
+            "condition: ExprP",
+            "then_branch: BlockExpr",
+            "else_branch: Option<BlockExpr>",
+        ],
+    )
+    .add_struct(
+        "Block",
+        [
+            "lbrace: Token",
+            "stmts: Vec<StmtP>",
+            "return_expr: Option<ExprP>",
+            "rbrace: Token",
+        ],
     ),
     # Stmt
     GenerateGroup("Stmt")
@@ -260,17 +278,7 @@ GENERATE = [
         "IndexAssign", ["expr: ExprP", "index: ExprP", "op: Token", "rhs: ExprP"]
     )
     .add_struct("Set", ["expr: ExprP", "name: Token", "op: Token", "rhs: ExprP"])
-    .add_struct("Block", ["lbrace: Token", "stmts: Vec<StmtP>", "rbrace: Token"])
-    .add_struct("Return", ["return_kw: Token", "expr: Option<ExprP>"])
-    .add_struct(
-        "If",
-        [
-            "if_kw: Token",
-            "condition: ExprP",
-            "then_branch: BlockStmt",
-            "else_branch: Vec<StmtP>",
-        ],
-    ),
+    .add_struct("Return", ["return_kw: Token", "expr: Option<ExprP>"]),
 ]