Move block statement to statement

include/ast.hpp

@@ -94,9 +94,8 @@ struct NullStmtNode : public StmtNode {
 };
 
 struct IfStmtNode : public StmtNode {
-  IfStmtNode(std::unique_ptr<ExprNode> expr,
-             std::unique_ptr<BlockStmtNode> then,
-             std::unique_ptr<BlockStmtNode> or_else = {})
+  IfStmtNode(std::unique_ptr<ExprNode> expr, std::unique_ptr<StmtNode> then,
+             std::unique_ptr<StmtNode> or_else = {})
       : predicate{std::move(expr)},
         then{std::move(then)},
         or_else{std::move(or_else)} {}
@@ -105,8 +104,8 @@ struct IfStmtNode : public StmtNode {
   virtual void Accept(ModifyingVisitor&) override;
 
   std::unique_ptr<ExprNode> predicate;
-  std::unique_ptr<BlockStmtNode> then;
-  std::unique_ptr<BlockStmtNode> or_else;
+  std::unique_ptr<StmtNode> then;
+  std::unique_ptr<StmtNode> or_else;
 };
 
 struct ReturnStmtNode : public StmtNode {

parser.y

@@ -66,6 +66,23 @@ extern std::unique_ptr<AstNode> program;
 %left '+' '-'
 %left '*' '/' '%'
 
+// Resolve the ambiguity in the "dangling-else" grammar.
+// Example: IF '(' expr ')' IF '(' expr ')' stmt • ELSE stmt
+// Yacc has two options to make, either shift or reduce:
+// Shift derivation
+//   stmt
+//   ↳ 13: IF '(' expr ')' stmt
+//                         ↳ 14: IF '(' expr ')' stmt • ELSE stmt
+// Reduce derivation
+//   stmt
+//   ↳ 14: IF '(' expr ')' stmt                         ELSE stmt
+//                         ↳ 13: IF '(' expr ')' stmt •
+//
+// Our goal is to find the closest IF for ELSE, so we tell Yacc to shift.
+// ELSE has a higher precendence than IF due to increasing precedence order.
+%precedence IF
+%precedence ELSE
+
 %start entry
 
 %%
@@ -74,12 +91,12 @@ entry: main_func {
   }
   ;
 
-  /* TODO: mix declarations and statements in compound statement */
 main_func: INT MAIN '(' ')' block {
     $$ = $5;
   }
   ;
 
+  /* TODO: mix declarations and statements in compound statement */
 block: '{' decls stmts '}' {
     $$ = std::make_unique<BlockStmtNode>($2, $3);
   }
@@ -109,8 +126,9 @@ stmts: stmts stmt {
 stmt: ';' { $$ = std::make_unique<NullStmtNode>(); }
     | RETURN expr ';' { $$ = std::make_unique<ReturnStmtNode>($2); }
     | expr ';' { $$ = std::make_unique<ExprStmtNode>($1); }
-    | IF '(' expr ')' block { $$ = std::make_unique<IfStmtNode>($3, $5); }
-    | IF '(' expr ')' block ELSE block { $$ = std::make_unique<IfStmtNode>($3, $5, $7); }
+    | block { $$ = $1; }
+    | IF '(' expr ')' stmt %prec IF { $$ = std::make_unique<IfStmtNode>($3, $5); }
+    | IF '(' expr ')' stmt ELSE stmt { $$ = std::make_unique<IfStmtNode>($3, $5, $7); }
     ;
 
 expr: ID { $$ = std::make_unique<IdExprNode>($1); }

test/codegen/if_else_nested_single_stmt.c

@@ -0,0 +1,12 @@
+int main() {
+  int i = 5;
+  if (i < 10)
+    if (i < 5)
+      i = 2;
+    else
+      i = 7;
+  else
+    i = 15;
+
+  return i;
+}

test/codegen/if_else_nested_single_stmt.exp

@@ -0,0 +1 @@
+7

test/codegen/if_else_single_stmt.c

@@ -0,0 +1,9 @@
+int main() {
+  int i = 2;
+  if (i > 0)
+    i = i - 1;
+  else
+    i = i + 1;
+
+  return i;
+}

test/codegen/if_else_single_stmt.exp

@@ -0,0 +1 @@
+1

test/codegen/if_single_stmt.c

@@ -0,0 +1,7 @@
+int main() {
+  int i = 2;
+  if (i > 0)
+    i = 0;
+
+  return i;
+}

test/codegen/if_single_stmt.exp

@@ -0,0 +1 @@
+0

test/typecheck/if_else_nested_single_stmt.c

@@ -0,0 +1,12 @@
+int main() {
+  int i = 5;
+  if (i < 10)
+    if (i < 5)
+      i = 2;
+    else
+      i = 7;
+  else
+    i = 15;
+
+  return i;
+}

test/typecheck/if_else_nested_single_stmt.exp

@@ -0,0 +1,34 @@
+(i: int =
+  5: int
+)
+(if
+  (<
+    i: int
+    10: int
+  ): int
+  (if
+    (<
+      i: int
+      5: int
+    ): int
+    (=
+      i: int
+      2: int
+    ): int
+  )
+  (else
+    (=
+      i: int
+      7: int
+    ): int
+  )
+)
+(else
+  (=
+    i: int
+    15: int
+  ): int
+)
+(ret
+  i: int
+)

test/typecheck/if_else_single_stmt.c

@@ -0,0 +1,9 @@
+int main() {
+  int i = 2;
+  if (i > 0)
+    i = i - 1;
+  else
+    i = i + 1;
+
+  return i;
+}

test/typecheck/if_else_single_stmt.exp

@@ -0,0 +1,28 @@
+(i: int =
+  2: int
+)
+(if
+  (>
+    i: int
+    0: int
+  ): int
+  (=
+    i: int
+    (-
+      i: int
+      1: int
+    ): int
+  ): int
+)
+(else
+  (=
+    i: int
+    (+
+      i: int
+      1: int
+    ): int
+  ): int
+)
+(ret
+  i: int
+)

test/typecheck/if_single_stmt.c

@@ -0,0 +1,7 @@
+int main() {
+  int i = 2;
+  if (i > 0)
+    i = i + 1;
+
+  return 0;
+}

test/typecheck/if_single_stmt.exp

@@ -0,0 +1,19 @@
+(i: int =
+  2: int
+)
+(if
+  (>
+    i: int
+    0: int
+  ): int
+  (=
+    i: int
+    (+
+      i: int
+      1: int
+    ): int
+  ): int
+)
+(ret
+  0: int
+)