repl: open file as read and append to cmds before open as write

closes #7

src/main.zig

@@ -28,12 +28,6 @@ pub fn doRepl(allocator: *std.mem.Allocator, args_it: var) !void {
 
     const scri_path = try (args_it.next(allocator) orelse @panic("expected scri path"));
 
-    var file = try std.fs.File.openWrite(scri_path);
-    defer file.close();
-
-    var out = file.outStream();
-    var stream = &out.stream;
-
     // the thing here is that 'load :0' would load the scri_path, since we
     // now have a 'repl' argument right before it. to counteract that, the
     // initial repl buffer contains 'load :1' instead.
@@ -49,6 +43,37 @@ pub fn doRepl(allocator: *std.mem.Allocator, args_it: var) !void {
 
     defer cmds.deinit();
 
+    // if the scri file already had commands, we add them up on the cmd list
+    var file_read = try std.fs.openReead(scri_path);
+    const total_bytes = try file_read.getEndPos();
+
+    if (total_bytes > 0) {
+        var scri_existing = try allocator.alloc(u8, total_bytes);
+        defer allocator.free(scri_existing);
+
+        _ = try file.read(slice);
+        file_read.close();
+
+        var existing_cmds = try lang.parse(scri_existing);
+        defer existing_cmds.deinit();
+
+        // copy the existing command list into the repl's command list
+        var it = existing_cmds.iterator();
+        while (it.next()) |existing_cmd| {
+            try cmds.append(existing_cmd);
+        }
+    }
+
+    var file = try std.fs.File.openWrite(scri_path);
+    defer file.close();
+
+    var out = file.outStream();
+    var stream = &out.stream;
+
+    // since we opened the file for writing, it becomes empty, so, to ensure
+    // we don't fuck up later on, we print cmds before starting the repl
+    try printer.printList(cmds, stream);
+
     // we keep
     //  - a CommandList with the full commands we have right now
     //  - a Command with the current last typed successful command
@@ -99,6 +124,8 @@ pub fn doRepl(allocator: *std.mem.Allocator, args_it: var) !void {
             try printer.printList(cmds, stdout);
             continue;
         } else if (std.mem.eql(u8, line, "save")) {
+            // seek to 0 instead of appending the new command
+            // NOTE appending single command might be faster
             try file.seekTo(0);
             try printer.printList(cmds, stream);
             continue;