$($@problem $1)$

;; A $*$SIMPLE$*$ one line text editor

;;

;; The screen looks like:

;;

;; ab$|$c

;;

;; where $|$ is the cursor.

;;

;; Typing characters inserts them.

;; left and right arrow moves cursor

;; delete removes character before cursor

$($@htdw Editor$)$

;; $=================$

;; Constants:

$($define WIDTH $200)$

$($define HEIGHT $20)$

$($define TEXT$-$SIZE $18)$

$($define TEXT$-$COLOR "BLACK"$)$

$($define CURSOR $($rectangle $120$ "solid" "red"$))$

$($define MTS $($empty$-$scene WIDTH HEIGHT$))$

;; $=================$

;; Data Definitions:

$($@htdd Editor$)$

$($define$-$struct editor $($pre post$))$

;; Editor is $($make$-$editor String String$)$

;; interp. $($make$-$editor pre post$)$ is an editor

;; pre is text before cursor

;; post is text after cursor

$($define ED$1($make$-$editor $""""))$

$($define ED$2($make$-$editor "abc" $"$d$"))$

$($define ED$3($make$-$editor "abcd" $""))$

$($define ED$4($make$-$editor $""$ "abcd"$))$

$($@dd$-$template$-$rules compound$)$ ;; $2$ fields

$($define $($fn$-$for$-$editor e$)$

$(...($editor$-$pre e$)$

$($editor$-$post e$)))$

;; $=================$

;; Functions:

$($@htdf run$-$editor$)$

$($@signature String $->$ Editor$)$

;; run an editor, with pre as the initial text preceding the cursor

$($@template$-$origin htdw$-$main$)$

$($define $($run$-$editor pre$)$

$($big$-$bang $($make$-$editor pre $"")$

$($to$-$draw render$)$ ; Editor $->$ Image

$($on$-$key handle$-$key$)))$ ; Editor KeyEvent $->$ Editor

$($@htdf render$)$

$($@signature Editor $->$ Image$)$

;; place text with cursor at left, middle edge of MTS

$($check$-$expect $($render $($make$-$editor $"$a$""$bc$"))$

$($overlay$/$align "left"

"middle"

$($beside $($text $"$a$"$ TEXT$-$SIZE TEXT$-$COLOR$)$

CURSOR

$($text $"$bc$"$ TEXT$-$SIZE TEXT$-$COLOR$))$

MTS$))$

;$($define $($render e$)$ MTS$)$ ;stub

$($@template$-$origin Editor$)$

$($@template

$($define $($render e$)$

$(...($editor$-$pre e$)$

$($editor$-$post e$))))$

Complete render

The starter contains an incomplete function design for render with an example and function template. Please comment out the stub and complete the function definition.