From 73d4aafdc458c93edb5823fac1def53ea79e309b Mon Sep 17 00:00:00 2001
From: rexim <reximkut@gmail.com>
Date: Sat, 25 Aug 2018 23:24:07 +0700
Subject: [PATCH] (#288) Extend ParseResult with error_cursor

---
 src/script/parser.c | 28 ++++++++++++++++------------
 src/script/parser.h |  8 ++++++--
 src/script_test.c   |  2 +-
 3 files changed, 23 insertions(+), 15 deletions(-)

diff --git a/src/script/parser.c b/src/script/parser.c
index 630ba9c3..bdc52455 100644
--- a/src/script/parser.c
+++ b/src/script/parser.c
@@ -25,7 +25,7 @@ struct ParseResult create_expr_from_str(const char *str,
 
     skip_whitespaces(str, cursor, n);
     if (*cursor >= n) {
-        return parse_failure("EOF");
+        return parse_failure("EOF", *cursor);
     }
 
     switch (str[*cursor]) {
@@ -38,17 +38,17 @@ struct ParseResult create_expr_from_str(const char *str,
 
         skip_whitespaces(str, cursor, n);
         if (*cursor >= n) {
-            return parse_failure("EOF");
+            return parse_failure("EOF", *cursor);
         }
 
         if (str[*cursor] != '.') {
-            return parse_failure("Expected .");
+            return parse_failure("Expected .", *cursor);
         }
         (*cursor)++;
 
         skip_whitespaces(str, cursor, n);
         if (*cursor >= n) {
-            return parse_failure("EOF");
+            return parse_failure("EOF", *cursor);
         }
 
         struct ParseResult cdr = create_expr_from_str(str, cursor, n);
@@ -58,11 +58,11 @@ struct ParseResult create_expr_from_str(const char *str,
 
         skip_whitespaces(str, cursor, n);
         if (*cursor >= n) {
-            return parse_failure("EOF");
+            return parse_failure("EOF", *cursor);
         }
 
         if (str[*cursor] != ')') {
-            return parse_failure("Expected )");
+            return parse_failure("Expected )", *cursor);
         }
 
         (*cursor)++;
@@ -72,7 +72,7 @@ struct ParseResult create_expr_from_str(const char *str,
 
     case '"': {
         /* TODO(#288): create_expr_from_str does not support strings */
-        return parse_failure("Strings are not supported");
+        return parse_failure("Strings are not supported", *cursor);
     }
 
     default: {
@@ -82,7 +82,7 @@ struct ParseResult create_expr_from_str(const char *str,
             const double x = strtod(nptr, &endptr);
 
             if (nptr == endptr) {
-                return parse_failure("Number expected");
+                return parse_failure("Number expected", *cursor);
             }
 
             *cursor += (size_t) (endptr - nptr);
@@ -90,12 +90,12 @@ struct ParseResult create_expr_from_str(const char *str,
             return parse_success(atom_as_expr(create_atom(ATOM_NUMBER, x)));
         } else if (isalpha(str[*cursor])) {
             /* TODO(#289): create_expr_from_str does not support symbols */
-            return parse_failure("Symbols are not supported");
+            return parse_failure("Symbols are not supported", *cursor);
         }
     }
     }
 
-    return parse_failure("Unexpected sequence of characters");
+    return parse_failure("Unexpected sequence of characters", *cursor);
 }
 
 struct ParseResult parse_success(struct Expr expr)
@@ -108,12 +108,16 @@ struct ParseResult parse_success(struct Expr expr)
     return result;
 }
 
-struct ParseResult parse_failure(const char *error)
+struct ParseResult parse_failure(const char *error,
+                                 size_t error_cursor)
 {
     struct ParseResult result = {
         .is_error = true,
-        .error = error
+        .error = error,
+        .error_cursor = error_cursor
     };
 
     return result;
 }
+
+/* TODO: there is no way to create a pretty report from ParseResult in case of an error */
diff --git a/src/script/parser.h b/src/script/parser.h
index 40b6c6a0..b2141ae3 100644
--- a/src/script/parser.h
+++ b/src/script/parser.h
@@ -9,12 +9,16 @@ struct ParseResult
     bool is_error;
     union {
         struct Expr expr;
-        const char *error;
+        struct {
+            const char *error;
+            size_t error_cursor;
+        };
     };
 };
 
 struct ParseResult parse_success(struct Expr expr);
-struct ParseResult parse_failure(const char *error);
+struct ParseResult parse_failure(const char *error,
+                                 size_t error_cursor);
 
 struct ParseResult create_expr_from_str(const char *str,
                                         size_t *cursor,
diff --git a/src/script_test.c b/src/script_test.c
index f45475cc..96c77fcd 100644
--- a/src/script_test.c
+++ b/src/script_test.c
@@ -15,7 +15,7 @@ int main(int argc, char *argv[])
     struct ParseResult result = create_expr_from_str(code, &cursor, n);
 
     if (result.is_error) {
-        fprintf(stderr, "[ERROR] %s", result.error);
+        fprintf(stderr, "[ERROR] %s on character %ld", result.error, result.error_cursor);
     } else {
         print_expr_as_sexpr(result.expr);
     }
-- 
2.44.0