For memory safety, the following data structures are opaque and only modified using functions described further down. I still find it useful to understand how they work under the hood.
addrvalues to access data they point to.
addrvalues in other types. They’re temporary.
handlevalues in other types.
Arrays: size-prefixed regions of memory containing multiple elements of a
single type. Contents are preceded by 4 bytes (32 bits) containing the
size of the array in bytes.
Slices: a pair of 32-bit addresses denoting a half-open
end) interval to live memory with a consistent lifetime.
Streams: strings prefixed by 32-bit
read indexes that the next
write or read goes to, respectively.
Invariant: 0 <=
By default, writes to a stream abort if it’s full. Reads to a stream abort if it’s empty.
The most useful functions from 400.mu and later .mu files. Look for definitions
ctags) to see type signatures.
abort: print a message in red on the bottom left of the screen and halt
check: fails current test if given boolean is false (
check-not: fails current test if given boolean isn’t false (
check-ints-equal: fails current test if given ints aren’t equal.
check-strings-equal: fails current test if given strings have different bytes.
check-stream-equal: fails current test if stream’s data doesn’t match string in its entirety. Ignores the stream’s read index.
check-array-equal: fails if an array’s elements don’t match what’s written in a whitespace-separated string.
check-next-stream-line-equal: fails current test if next line of stream until newline doesn’t match string.
handle-equal?: checks if two handles point at the identical address. Does
not compare payloads at their respective addresses.
array-equal?: checks if two arrays (of ints only for now) have identical
string-equal?: compares two strings.
stream-data-equal?: compares a stream with a string.
next-stream-line-equal?: compares with string the next line in a stream, from
read index to newline.
slice-empty?: checks if the
endof a slice are equal.
slice-equal?: compares a slice with a string.
slice-starts-with?: compares the start of a slice with a string.
stream-full?: checks if a write to a stream would abort.
stream-empty?: checks if a read from a stream would abort.
populate: allocates space for
nobjects of the appropriate type.
copy-array: allocates enough space and writes out a copy of an array of some type.
slice-to-string: allocates space for an array of bytes and copies the slice into it.
populate-stream: allocates space in a stream for
nobjects of the appropriate type.
write-to-stream: writes arbitrary objects to a stream of the appropriate type.
read-from-stream: reads arbitrary objects from a stream of the appropriate type.
stream-to-array: allocates just enough space and writes out a stream’s
data between its read index (inclusive) and write index (exclusive).
clear-stream: resets everything in the stream to
rewind-stream: resets the read index of the stream to
0 without modifying
write: writes a string into a stream of bytes. Doesn’t support streams of other types.
try-write: writes a string into a stream of bytes if possible. Doesn’t support streams of other types.
write-stream: concatenates one stream into another.
write-slice: writes a slice into a stream of bytes.
append-byte: writes a single byte into a stream of bytes.
append-byte-hex: writes textual representation of lowest byte in hex to a stream of bytes. Does not write a ‘0x’ prefix.
read-byte: reads a single byte from a stream of bytes.
read-grapheme: reads a single unicode grapheme (up to 4 bytes containing a single code-point encoded in utf-8) from a stream of bytes.
hex-int?: checks if a slice contains an int in hex. Supports ‘0x’ prefix.
parse-hex-int: reads int in hex from string
parse-hex-int-from-slice: reads int in hex from slice
parse-array-of-ints: reads in multiple ints in hex, separated by whitespace.
hex-digit?: checks if byte is in [0, 9] or [a, f] (lowercase only)
decimal-digit?: checks if byte is in [0, 9]
pixel-on-real-screen draws a single pixel in one of 256 colors.
All text-mode screen primitives require a screen object, which can be either the real screen on the computer or a fake screen for tests.
The real screen on the Mu computer can currently display only ASCII characters, though it’s easy to import more of the font. There is only one font, and it’s mostly fixed-width, with graphemes being either 8 or 16 pixels wide.
draw-grapheme: draws a single grapheme at a given coordinate, with given foreground and background colors.
draw-graphemeand can also handle newlines assuming text is printed left-to-right, top-to-bottom.
draw-text-rightward: draws a single line of text, stopping when it reaches either the provided bound or the right screen margin.
draw-text-rightward-over-full-screen: does not provide a bound.
draw-text-wrapping-right-then-down: draws multiple lines of text on screen with simplistic word-wrap (no hyphenation) within (x, y) bounds.
Similar primitives for writing text top-to-bottom, left-to-right.
Screens remember the current cursor position.
draw-cursor: highlights the current position of the cursor. Programs must pass in the grapheme to draw at the cursor position, and are responsible for clearing the highlight when the cursor moves.
move-cursor-down. These primitives always silently fail if the desired movement would go out of screen bounds.
move-cursor-rightward-and-downward: move cursor one grapheme to the right
Assertions for tests:
check-screen-row: compare a screen from the left margin of a given row index with a string. The row index counts downward from 0 at the top of the screen. String can be smaller or larger than a single row, and defines the region of interest. Strings longer than a row wrap around to the left margin of the next screen row. Currently assumes text is printed left-to-right on the screen.
check-screen-row-from: compare a fragment of a screen (left to write, top to bottom) starting from a given (x, y) coordinate with an expected string. Currently assumes text is printed left-to-right and top-to-bottom on the screen.
check-background-color-in-screen-row: unlike previous functions, this doesn’t check screen contents, only background color. Ignores background color where expected string contains spaces, and compares background color where expected string does not contain spaces. Never compares the character at any screen location.
read-key reads a single key from the keyboard and returns it if it exists.
Returns 0 if no key has been pressed.
read-mouse-event returns a recent change in x and y coordinate.
Mu doesn’t currently support interrupt-based mouse events.
load-sector synchronously reads a single sector from a disk of persistent
storage. The disk must follow the ATA specification with a 28-bit sector
address. Each sector is 512 bytes. Therefore, Mu currently supports ATA hard
disks of up to 128GB capacity.
store-sector synchronously writes a single sector to disk.
Mu doesn’t currently support asynchronous transfers to or from a disk.