Nicer plus_minus

resources/examples/plus_minus.c3

@@ -7,35 +7,78 @@ fault TokenResult
 	NO_MORE_TOKENS
 }
 
+
+// While we could have written this with libc
+// the C way, let's showcase some features added to C3.
+fn void main(char[][] args)
+{
+	// Grab a string from stdin
+	String s = io::stdin().getline();
+	// Delete it at scope end [defer]
+	defer s.destroy();
+
+	// Grab the string as a slice.
+	char[] numbers = s.str();
+
+	// Track our current value
+	int val = 0;
+
+	// Is the current state an add?
+	bool add = true;
+
+	while (try char[] token = read_next(&numbers))
+	{
+		// We're assuming well formed input here
+		// so just use atoi.
+		int i = libc::atoi(token.ptr);
+
+		// This value is either added or subtracted from the sum.
+		val = add ? val + i : val - i;
+
+		// Read an optional token.
+		char[]! op = read_next(&numbers);
+
+		// If it's an error, then we're done.
+		if (catch op) break;
+
+		// Let's process the operator
+		switch (op)
+		{
+			case "+":
+				add = true;
+			case "-":
+				add = false;
+			default:
+				io::println("Failed to parse expression.");
+				return;
+		}
+	}
+	io::printfln("%d", val);
+}
+
 fn char[]! read_next(char[]* remaining)
 {
-	// Skip spaces.
-	while (remaining.len > 0 && (*remaining)[0] == ' ') *remaining = (*remaining)[1..];
+	while (remaining.len > 0 && (*remaining)[0] == ' ')
+	{
+		// Make the slice smaller
+		*remaining = (*remaining)[1..];
+	}
+
+	// Store the beginning of the parse
 	char* ptr_start = remaining.ptr;
 	usize len = 0;
 	while (remaining.len > 0 && (*remaining)[0] != ' ')
 	{
+		// Increase length
 		len++;
+
+		// And make the slice smaller
 		*remaining = (*remaining)[1..];
 	}
+
+	// If it's a zero length token, return an optional result.
 	if (!len) return TokenResult.NO_MORE_TOKENS!;
+
+	// Otherwise create a slice from the pointer start and length.
 	return ptr_start[:len];
 }
-
-fn void main(char[][] args)
-{
-	String s = io::stdin().getline();
-	defer s.destroy();
-	char[] numbers = s.str();
-	int val = 0;
-	bool add = true;
-	while (try char[] token = read_next(&numbers))
-	{
-		int i = libc::atoi(token.ptr);
-		val = add ? val + i : val - i;
-		char[]! op = read_next(&numbers);
-		if (catch op) break;
-		add = op[0] == '+';
-	}
-	io::printfln("%d", val);
-}