Added some helpful comments to the creature command

.gitignore

@@ -0,0 +1 @@
+/cmd/creature/creature

cmd/creature/examples/echo

@@ -0,0 +1,10 @@
+---
+0 0
+F
+
+0 1
+F
+
+0 1
+0 0
+E

cmd/creature/main.go

@@ -0,0 +1,112 @@
+package main
+
+import "io"
+import "os"
+import "fmt"
+import "bufio"
+import "strconv"
+import cre "git.tebibyte.media/sashakoshka/creature"
+
+func main() {
+	if len(os.Args) != 2 {
+		logLine("ERR file unspecified")
+		os.Exit(1)
+	}
+
+	file, err := os.Open(os.Args[1])
+	if err != nil {
+		logLine("ERR could not open file: " + err.Error())
+		os.Exit(1)
+	}
+
+	program, block, err := readFile(file)
+	if err != nil {
+		logLine("ERR could not read file: " + err.Error())
+		os.Exit(1)
+	}
+
+	machine := cre.Machine[int]{}
+
+	machine.LoadProgram(program)
+	machine.LoadMemory(block)
+
+	machine.Register(0, read)
+	machine.Register(1, write)
+
+	err = machine.Execute(0)
+	if err != nil {
+		logLine("XXX machine failed: " + err.Error())
+		os.Exit(1)
+	}
+}
+
+// read implements a basic input function for the creature. It waits until it
+// has recieved one byte of user input, and then pushes that byte onto the
+// stack.
+func read(machine *cre.Machine[int]) (stop bool) {
+	ch := []byte{0}
+	os.Stdin.Read(ch)
+	machine.Push(int(ch[0]))
+	return
+}
+
+// write implements a basic output function for the creature. It pops one byte
+// off of the stack, and writes it to stdout.
+func write(machine *cre.Machine[int]) (stop bool) {
+	print(string(rune(machine.Pop())))
+	return
+}
+
+// logLine prints a message to stderr.
+func logLine(message ...any) {
+	fmt.Fprintln(os.Stderr, message...)
+}
+
+// readFile reads data from an io.Reader into a program slice and a block slice.
+// Data in the file is represented by signed hexidecimal numbers, separated by
+// whitespace. Three dashes (---) divide the block data from the program data.
+// See examples/echo.
+func readFile(reader io.Reader) (program []int, block []int, err error) {
+	scanner := bufio.NewScanner(reader)
+	scanner.Split(bufio.ScanWords)
+
+	blockLen := 0
+	block = make([]int, 8)
+	for scanner.Scan() {
+		if scanner.Text() == "---" {
+			break
+		}
+		if blockLen >= len(block) {
+			newSlice := make([]int, len(block)*2)
+			copy(newSlice, block)
+			block = newSlice
+		}
+		var number int64
+		number, err = strconv.ParseInt(scanner.Text(), 16, 64)
+		if err != nil {
+			return
+		}
+		block[blockLen] = int(number)
+		blockLen++
+	}
+	block = block[:blockLen]
+
+	programLen := 0
+	program = make([]int, 8)
+	for scanner.Scan() {
+		if programLen >= len(program) {
+			newSlice := make([]int, len(program)*2)
+			copy(newSlice, program)
+			program = newSlice
+		}
+		var number int64
+		number, err = strconv.ParseInt(scanner.Text(), 16, 64)
+		if err != nil {
+			return
+		}
+		program[programLen] = int(number)
+		programLen++
+	}
+	program = program[:programLen]
+	return
+}

creature_test.go

@@ -118,7 +118,6 @@ func TestComparison(test *testing.T) {
 		PUSH, 54,
 		PUSH, 6,
 		NEQ,
-		
 	}, nil, test)
 
 	neqResult := machine.Pop()

examples/echo.go

@@ -1,3 +1,4 @@
+//go:build ignore
 // +build ignore
 
 package main
@@ -25,7 +26,9 @@ func main () {
 	machine.Register(0, read)
 	machine.Register(1, write)
 	err := machine.Execute(0)
-	if err != nil { panic(err.Error()) }
+	if err != nil {
+		panic(err.Error())
+	}
 }
 
 func read(machine *cre.Machine[int]) (stop bool) {

examples/psychiatrist.go

@@ -1,3 +1,4 @@
+//go:build ignore
 // +build ignore
 
 package main
@@ -127,7 +128,9 @@ func main () {
 	machine.Register(1, write)
 
 	err := machine.Execute(0)
-	if err != nil { panic(err.Error()) }
+	if err != nil {
+		panic(err.Error())
+	}
 }
 
 func read(machine *cre.Machine[int]) (stop bool) {