Is CSS Turing complete

Question

CSS isn t  insofar as I know  Turing complete   But my knowledge of CSS is very limited      Is CSS Turing complete  Are any of the existing draft or committees considering language features that might enable Turing completeness if it isn t right now

User · Answer

The fundamental issue here is that any machine written in HTML CSS cannot evaluate infinitely many steps  i e there can be no  real  recursion  unless the code is infinitely long  And the question will this machine reach configuration H in n steps or less is always answerable if n is finite

User · Answer

As per this article  it s not  The article also argues that it s not a good idea to make it one   To quote from one of the comments      So  I do not believe that CSS is   turing complete  There is no   capability to define a function in   CSS  In order for a system to be   turing-complete it has to be possible   to write an interpreter  a function   that interprets expressions that   denote programs to execute  CSS has no   variables that are directly accessible   to the user  so you cannot even model   the structure that represents the   program to be interpreted in CSS

User · Answer

One aspect of Turing completeness is the halting problem   This means that  if CSS is Turing complete  then there s no general algorithm for determining whether a CSS program will finish running or loop forever   But we can derive such an algorithm for CSS  Here it is    If the stylesheet doesn t declare any animations  then it will halt  If it does have animations  then    If any animation-iteration-count is infinite  and the containing selector is matched in the HTML  then it will not halt  Otherwise  it will halt     That s it  Since we just solved the halting problem for CSS  it follows that CSS is not Turing complete    Other people have mentioned IE 6  which allows for embedding arbitrary JavaScript expressions in CSS  that will obviously add Turing completeness  But that feature is non-standard  and nobody in their right mind uses it anyway      Daniel Wagner brought up a point that I missed in the original answer  He notes that while I ve covered animations  other parts of the style engine such as selector matching or layout can lead to Turing completeness as well  While it s difficult to make a formal argument about these  I ll try to outline why Turing completeness is still unlikely to happen   First  Turing complete languages have some way of feeding data back into itself  whether it be through recursion or looping  But the design of the CSS language is hostile to this feedback     media queries can only check properties of the browser itself  such as viewport size or pixel resolution  These properties can change via user interaction or JavaScript code  e g  resizing the browser window   but not through CSS alone    before and   after pseudo-elements are not considered part of the DOM  and cannot be matched in any other way  Selector combinators can only inspect elements above and before the current element  so they cannot be used to create dependency cycles  It s possible to shift an element away when you hover over it  but the position only updates when you move the mouse    That should be enough to convince you that selector matching  on its own  cannot be Turing complete  But what about layout   The modern CSS layout algorithm is very complex  with features such as Flexbox and Grid muddying the waters  But even if it were possible to trigger an infinite loop with layout  it would be hard to leverage this to perform useful computation  That s because CSS selectors inspect only the internal structure of the DOM  not how these elements are laid out on the screen  So any Turing completeness proof using the layout system must depend on layout alone   Finally  ndash  and this is perhaps the most important reason  ndash  browser vendors have an interest in keeping CSS not Turing complete  By restricting the language  vendors allow for clever optimizations that make the web faster for everyone  Moreover  Google dedicates a whole server farm to searching for bugs in Chrome  If there were a way to write an infinite loop using CSS  then they probably would have found it already

User · Answer

Turing-completeness is not only about  defining functions  or  have ifs loops etc   For example  Haskell doesn t have  loop   lambda-calculus don t have  ifs   etc     For example  this site  http   experthuman com programming-with-nothing  The author uses Ruby and create a  FizzBuzz  program with only closures  no strings  numbers  or anything like that      There are examples when people compute some arithmetical functions on Scala using only the type system  So  yes  in my opinion  CSS3 HTML is turing-complete  even if you can t exactly do any real computation with then without becoming crazy

User · Answer

CSS is not a programming language  so the question of turing-completeness is a meaningless one  If programming extensions are added to CSS such as was the case in IE6 then that new synthesis is a whole different thing   CSS is merely a description of styles  it does not have any logic  and its structure is flat

User · Answer

You can encode Rule 110 in CSS3  so it s Turing-complete so long as you consider an appropriate accompanying HTML file and user interactions to be part of the    execution    of CSS  A pretty good implementation is available  and another implementation is included here    x000D   x000D  body   x000D      -webkit-animation  bugfix infinite 1s  x000D      margin  0 5em 1em  x000D    x000D   -webkit-keyframes bugfix   from   padding  0    to   padding  0      x000D   x000D     x000D     111 110 101 100 011 010 001 000 x000D      0   1   1   0   1   1   1   0 x000D      x000D   x000D  body  gt  input   x000D      -webkit-appearance  none  x000D      display  block  x000D      float  left  x000D      border-right  1px solid  ddd  x000D      border-bottom  1px solid  ddd  x000D      padding  0px 3px  x000D      margin  0  x000D      font-family  Consolas   Courier New   monospace  x000D      font-size  7pt  x000D    x000D  body  gt  input  before   x000D      content   0   x000D    x000D   x000D  p   x000D      font-family  Verdana  sans-serif  x000D      font-size  9pt  x000D      margin-bottom  0 5em  x000D    x000D   x000D  body  gt  input nth-of-type -n 30    border-top  1px solid  ddd    x000D  body  gt  input nth-of-type 30n 1    border-left  1px solid  ddd  clear  left    x000D   x000D  body  gt  input  before   content   0     x000D   x000D  body  gt  input checked  before   content   1     x000D  body  gt  input checked   background   afa  important    x000D   x000D   x000D  input not  checked    x000D                                                                       x000D          input  before   x000D      content   1   x000D    x000D  input not  checked    x000D                                                                       x000D          input   x000D      background   fa0  x000D    x000D   x000D   x000D  input checked   x000D                                                                     x000D          input  before   x000D      content   1  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User · Answer

This answer is not accurate because it mix description of UTM and UTM itself  Universal Turing Machine    We have good answer but from different perspective and it do not show directly flaws in current top answer     First of all we can agree that human can work as UTM  This mean if we do  CSS   Human    UTM   Then CSS part is useless because all work can be done by Human who will do UTM part  Act of clicking can be UTM  because you do not click at random but only in specific places   Instead of CSS I could use this text  Rule 110    000 - gt  0 001 - gt  1 010 - gt  1 011 - gt  1 100 - gt  0 101 - gt  1 110 - gt  1 111 - gt  0   To guide my actions and result will be same  This mean this text UTM  No this is only input  description  that other UTM  human or computer  can read and run  Clicking is enough to run any UTM     Critical part that CSS lack is ability to change of it own state in arbitrary way  if CSS could generate clicks then it would be UTM  Argument that your clicks are  crank  for CSS is not accurate because real  crank  for CSS is Layout Engine that run it and it should be enough to prove that CSS is UTM

[css] Is CSS Turing complete?

Examples related to css

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