// ascii — rune-class predicates and case folding for the ASCII range.
// Matches Hare's ascii::isdigit family (rune-taking signature). Runes
// outside 0..127 always answer `false`. The lexer hot path uses these
// inline; they are expected to inline to a couple of compares.

export fn isdigit(c: rune) bool = {
	if (c < 48) { return false; };
	if (c > 57) { return false; };
	return true;
};

export fn isupper(c: rune) bool = {
	if (c < 65) { return false; };
	if (c > 90) { return false; };
	return true;
};

export fn islower(c: rune) bool = {
	if (c < 97) { return false; };
	if (c > 122) { return false; };
	return true;
};

export fn isalpha(c: rune) bool = {
	if (isupper(c)) { return true; };
	return islower(c);
};

export fn isalnum(c: rune) bool = {
	if (isalpha(c)) { return true; };
	return isdigit(c);
};

// isspace — the C/Hare set: space, tab, NL, VT, FF, CR.
export fn isspace(c: rune) bool = {
	if (c == 32) { return true; };	// ' '
	if (c == 9)  { return true; };	// '\t'
	if (c == 10) { return true; };	// '\n'
	if (c == 11) { return true; };	// '\v'
	if (c == 12) { return true; };	// '\f'
	if (c == 13) { return true; };	// '\r'
	return false;
};

export fn isxdigit(c: rune) bool = {
	if (isdigit(c)) { return true; };
	if (c >= 65) {
		if (c <= 70) { return true; };	// 'A'..'F'
	};
	if (c >= 97) {
		if (c <= 102) { return true; };	// 'a'..'f'
	};
	return false;
};

// digitval — value of `c` as a hex/decimal digit. void variant means
// `c` isn't a hex digit. Useful when scanning numeric literals.
export fn digitval(c: rune) (i32 | void) = {
	if (isdigit(c)) { return (c - 48): i32; };
	if (c >= 65) {
		if (c <= 70) { return ((c - 65) + 10): i32; };
	};
	if (c >= 97) {
		if (c <= 102) { return ((c - 97) + 10): i32; };
	};
	return;
};

// isidstart / isidpart — identifier classes used by the lexer.
// Alpha or '_' starts; alnum or '_' continues.
export fn isidstart(c: rune) bool = {
	if (isalpha(c)) { return true; };
	if (c == 95) { return true; };	// '_'
	return false;
};

export fn isidpart(c: rune) bool = {
	if (isalnum(c)) { return true; };
	if (c == 95) { return true; };
	return false;
};

// tolower / toupper — fold ASCII case. Non-letters pass through.
export fn tolower(c: rune) rune = {
	if (isupper(c)) { return c + 32; };
	return c;
};

export fn toupper(c: rune) rune = {
	if (islower(c)) { return c - 32; };
	return c;
};