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pub const Token = struct {
start: usize,
end: usize,
type: Type,
pub const Type = union(enum) {
LeftParen,
RightParen,
IntegerLiteral: usize,
Plus,
Invalid,
Eof,
};
};
source: []const u8,
last_end: usize = 0,
pos: usize = 0,
pub fn next(self: *Self) ?Token {
return s: switch (self.eat() orelse return self.create(.Eof)) {
'(' => self.create(.LeftParen),
')' => self.create(.RightParen),
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9' => |d| self.integerLiteral(d),
'+' => self.create(.Plus),
' ' => {
self.last_end = self.pos;
continue :s (self.eat() orelse return self.create(.Eof));
},
else => self.create(.Invalid),
};
}
fn integerLiteral(self: *Self, first: u8) Token {
var value: usize = @intCast(digitValue(first).?);
while (digitValue(self.peek())) |d| {
_ = self.eat();
value = value *| 10 +| d;
}
return self.create(.{ .IntegerLiteral = value });
}
fn create(self: *Self, tajp: Token.Type) Token {
const start = self.last_end;
self.last_end = self.pos;
return .{ .start = start, .end = self.pos, .type = tajp };
}
fn eat(self: *Self) ?u8 {
const token = self.peek();
if (token != null) self.pos += 1;
return token;
}
fn peek(self: *Self) ?u8 {
return if (self.pos < self.source.len) self.source[self.pos] else null;
}
const Self = @This();
fn digitValue(c: ?u8) ?u8 {
return switch (c orelse return null) {
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9' => c.? - '0',
else => null,
};
}
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