Viw, the ghetto editor

VI Worsened, a lightweight and fun VI clone. Inspired by the 6-domino-cascade from the React world.

DEMO

https://vimeo.com/205701269

Dependencies

• gcc
• ncurses

# Fedora
sudo dnf install ncurses-devel

# Debian/Ubuntu
sudo apt-get install libncurses5-dev

Installation & usage

git clone https://github.com/lpan/viw
cd viw/
make build
./viw [filename]

Using mingw compiler on Windows, you need to install mingw-w64-x86_64-ncurses

pacman -S mingw-w64-x86_64-ncurses
mingw32-make build

Supported keybindings

• j Cursor down
• k Cursor up
• h Cursor left
• l Cursor right
• 0 Cursor to the beginning of the line
• $ Cursor to the end of the line
• i Insert before
• I Insert at the beginning of the line
• a Insert after
• A Insert at the end of the line
• o Append line then insert
• O Prepend line then insert
• dd Delete line under the cursor
• gg Go to the first line of the file
• G Go the last line of the file
• u Undo
• r Redo (Unstable)

Supported EX mode commands

• :q quit
• :w save
• :wq save then quit

Hacking

Feel free to contribute! :)

How does it work

1. initiate the state

• Read file to buffer.
• Set up interface with ncurses

2. Listen to keyboard events.

• Each supported keybinding is mapped to a method that mutates the buffer

3. Run update_state(st) and render_update(st)

• Similar to selectors in redux, update_state(state_t *st) will update all the computed properties (such as cursor position, rows to be displayed on the screen, etc) according to the new mutated buffer state.
• render_update(state_t *st) will actually render everything on the screen according to the result from update_state().

4. Goto step 2

Undo & Redo

Viw's undo & redo functionality is based on the state machine replication principle

1. Initialization:
   • Deep clone the initial buffer.
   • Initialize two stacks (history stack and redo stack).
2. Capture all state-mutating functions and their payloads and push it on to the history stack.
3. When the user hits undo:
   • Pop the history stack and the push the result onto redo stack.
   • Clone the initial buffer and apply all the commands saved in the history stack on top of it.
4. When the user hits redo:
   • Pop the redo stack and apply the command immediately onto the current buffer.
5. Clear the redo stack when a command gets pushed to the history stack by the user.

See https://github.com/lpan/viw/blob/master/src/controller.c#L152 for more details

Hierarchy of the states

Our main state object has two children states, namely buffer and screen. This seperation makes it easier to perform unit tests against the buffer. It also facilitates the migration to a different rendering library in the future.

The State

• The parent state stores computed states that depend on the buffer and/or screen. Those states include cursor positions, aount of space reserved for line numbers, etc.

The Buffer

• The buffer is represented as a two dimensional doubly linked list. This allows conatant time line/char deletion and insertion. Go to buffer.h for more information.
• Buffer is only allowed to be modified by the methods declared in buffer.h

The Screen

• The screen is the state of the interface between viw and GNU ncurses. It stores information such as pointers to the ncurses windows, etc. You can learn more about it at screen.h.