Expression History

The Lua interpreter can save typed lines. But when a partial line is written the saved history is not exactly what was typed. This is most apparent when the line is an expression that has to be rewritten as a valid statement.

This patch will save the original line as typed in the history. It is written agains Lua 5.3.0. It is not needed in Lua 5.3.1.

A full-featured interactive Lua frontend can be had with luaprompt. No patching necessary.

expression_history.diff

diff --git a/src/lua.c b/src/lua.c
index 34a3900..d007d34 100644
--- a/src/lua.c
+++ b/src/lua.c
@@ -327,19 +327,23 @@ static int pushline (lua_State *L, int firstline) {
 
 /*
 ** Try to compile line on the stack as 'return <line>'; on return, stack
-** has either compiled chunk or original line (if compilation failed).
+** has either compiled chunk or error message (if compilation failed).
+** The original line remains on the stack.
 */
-static int addreturn (lua_State *L) {
+static int addreturn (lua_State *L, int idx) {
   int status;
   size_t len; const char *line;
   lua_pushliteral(L, "return ");
-  lua_pushvalue(L, -2);  /* duplicate line */
+  lua_pushvalue(L, idx);  /* duplicate line */
   lua_concat(L, 2);  /* new line is "return ..." */
   line = lua_tolstring(L, -1, &len);
-  if ((status = luaL_loadbuffer(L, line, len, "=stdin")) == LUA_OK)
-    lua_remove(L, -3);  /* remove original line */
-  else
+  if ((status = luaL_loadbuffer(L, line, len, "=stdin")) == LUA_OK) 
+    lua_remove(L, -2);  /* remove new line */
+  else {
     lua_pop(L, 2);  /* remove result from 'luaL_loadbuffer' and new line */
+    line = lua_tolstring(L, idx, &len);  /* get what it has */
+    status = luaL_loadbuffer(L, line, len, "=stdin");  /* try it */
+  }
   return status;
 }
 
@@ -349,9 +353,7 @@ static int addreturn (lua_State *L) {
 */
 static int multiline (lua_State *L) {
   for (;;) {  /* repeat until gets a complete statement */
-    size_t len;
-    const char *line = lua_tolstring(L, 1, &len);  /* get what it has */
-    int status = luaL_loadbuffer(L, line, len, "=stdin");  /* try it */
+    int status = addreturn(L, 1);
     if (!incomplete(L, status) || !pushline(L, 0))
       return status;  /* cannot or should not try to add continuation line */
     lua_pushliteral(L, "\n");  /* add newline... */
@@ -372,8 +374,7 @@ static int loadline (lua_State *L) {
   lua_settop(L, 0);
   if (!pushline(L, 1))
     return -1;  /* no input */
-  if ((status = addreturn(L)) != LUA_OK)  /* 'return ...' did not work? */
-    status = multiline(L);  /* try as command, maybe with continuation lines */
+  status = multiline(L);  /* try as command, maybe with continuation lines */
   lua_saveline(L, 1);  /* keep history */
   lua_remove(L, 1);  /* remove line from the stack */
   lua_assert(lua_gettop(L) == 1);