diff --git a/source/md.c b/source/md.c
index 5cf5c7b..e46acb8 100644
--- a/source/md.c
+++ b/source/md.c
@@ -206,6 +206,7 @@ MD_WIN32_Release(void *ptr, MD_u64 size){
 # include <fcntl.h>
 # include <unistd.h>
 # include <sys/syscall.h>
+# include <sys/mman.h>
 // NOTE(mal): To get these constants I need to #define _GNU_SOURCE,
 // which invites non-POSIX behavior I'd rather avoid
 # ifndef O_PATH
@@ -2992,10 +2993,10 @@ MD_ExprBakeOperatorTableFromList(MD_Arena *arena, MD_ExprOperatorList *list){
     return(result);
 }
 
-MD_FUNCTION MD_ExprNode*
+MD_FUNCTION MD_ExprParseResult
 MD_ExprParse(MD_Arena *arena, MD_ExprOperatorTable *op_table,
              MD_Node *first, MD_Node *one_past_last){
-    MD_ExprNode *result = 0;
+    MD_ExprParseResult result = {0};
     // TODO(allen): @expr_parser
     return(result);
 }
diff --git a/source/md.h b/source/md.h
index 4791288..06092c2 100644
--- a/source/md.h
+++ b/source/md.h
@@ -681,9 +681,11 @@ struct MD_ParseResult
 
 typedef enum MD_ExprOperatorKind
 {
+    // TODO(mal): We could improve this naming scheme
     MD_ExprOperatorKind_Prefix,
     MD_ExprOperatorKind_Postfix,
     MD_ExprOperatorKind_Binary,
+    MD_ExprOperatorKind_BinaryRightAssociative,
 } MD_ExprOperatorKind;
 
 typedef struct MD_ExprOperator MD_ExprOperator;
@@ -715,6 +717,7 @@ struct MD_ExprOperatorTable
 {
     // TODO(allen): @expr_parser fill this in however needed
     int foo;
+    MD_MessageList errors;
 };
 
 typedef struct MD_ExprNode MD_ExprNode;
@@ -729,6 +732,13 @@ struct MD_ExprNode
     MD_Node *md_op_node;
 };
 
+typedef struct MD_ExprParseResult MD_ExprParseResult;
+struct MD_ExprParseResult
+{
+    MD_ExprNode *node;
+    MD_MessageList errors;
+};
+
 //~ String Generation Types
 
 typedef MD_u32 MD_GenerateFlags;
@@ -1096,8 +1106,8 @@ MD_FUNCTION void   MD_ExprOperatorPush(MD_Arena *arena, MD_ExprOperatorList *lis
 MD_FUNCTION MD_ExprOperatorTable MD_ExprBakeOperatorTableFromList(MD_Arena *arena,
                                                                   MD_ExprOperatorList *list);
 
-MD_FUNCTION MD_ExprNode* MD_ExprParse(MD_Arena *arena, MD_ExprOperatorTable *op_table,
-                                      MD_Node *first, MD_Node *one_past_last);
+MD_FUNCTION MD_ExprParseResult MD_ExprParse(MD_Arena *arena, MD_ExprOperatorTable *op_table,
+                                            MD_Node *first, MD_Node *one_past_last);
 
 //~ String Generation