A Text Editor

Written by Luke Boswell

Example code

working with the terminal

• introduce basic-cli dependency
• background on the terminal
  • ANSI escape codes control the cursor and colors etc
  • Raw mode to read keypresses
• handle any errors using a tag union, and print to STDERR
• using ANSI escape codes manually
  • clear the window
  • write out a colored “Hello World” message

a simple TUI window

• introduce roc-ansi dependency
• minimum code needed to create a “window” with a cursor
• handle ESC keypress to close and exit
• introduce Model and how state is passed between draws
• introduce a cursor, move it around

read a file

• parse file path from command line arguments
• check file exists, and read contents
• parse file into Graphemes (unicode text segmentation)

display file contents

• introduce a Piece Table
• split file into lines splitIntoLines : List Grapheme, List Grapheme, List (List Grapheme) -> List (List Grapheme)
• draw lines of file into a viewport on the screen
• only use a single piece table in state i.e.

fileContents: { original : List Grapheme, added : List Grapheme, table : List Entry,}

text editor

• handle vertical scrolling of text in the viewport using a lineOffset
• map cursor position on screen to a position in the file calculateCursorIndex : List (List Grapheme), U32, {row : I32, col : I32 }, U64 -> U64
• keep changes between user input in state, use a history and future list to keep track of multipl piece tables
• implement CTRL-S to save file contents to disk
• implement typing to insert text
• implement CTRL-Z to undo, and CRTl-Y to redo