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    <p>You use pattern matching for that: </p> <pre><code>advance :: DA -&gt; State -&gt; String -&gt; State advance (start, step, accept) fromState chars = .... </code></pre> <p>The <code>type</code> keyword just introduces <a href="http://en.wikibooks.org/wiki/Haskell/Type_declarations#type_for_making_type_synonyms" rel="nofollow noreferrer">type synonyms</a>. <code>DA</code> is just a synonym for a triple <code>(Integer, Integer -&gt; Char -&gt; Integer, Integer -&gt; Bool)</code>.</p> <p>Your naming is confusing. <code>delta</code> in the definition of <code>a</code> automaton is a state transition function, but in the definition of <code>toDA</code> function, a parameter named <code>delta</code> is a list. <code>ListDA</code> type is also just a synonym for a triple (a different one - of a state, a list of transitions, and a list of acceptable states).</p> <p>Here is how this can be coded, using recursion for loops:</p> <pre><code>advance (_, step, _) fromState chars = go fromState chars where go s [] = ... -- stop, and produce the state as the answer, -- when the input string (list of chars) has ended go s (c:cs) = -- if not, then let s2 = step s c -- make one step in go ....... -- and loop with new values </code></pre> <p>Notice we have no need here for the <code>start</code> or <code>accept</code> variables, so we can use the anonymous variable pattern <code>_</code> there. Also, <code>step</code> is a function of type <code>State -&gt; Char -&gt; State</code>, and that dictates the order of arguments used in the function call there. I.e. it accepts a state and a character, and produces a new state.</p> <p>If you don't know Haskell at all, you will likely benefit from reading (and working through) a good tutorial, <a href="http://learnyouahaskell.com/" rel="nofollow noreferrer">like this one</a>.</p> <p>Lastly, since you've said you're "not familiar with posting questions in a forum", please read about <a href="https://meta.stackexchange.com/a/5235/172601">accepting answers</a>, and <a href="https://meta.stackexchange.com/questions/7931/faq-for-stack-exchange-sites">FAQ</a> in general.</p>
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    1. POHow Can I call a function, that is integrated in a type in Haskell?
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    1. COthanks for your fast support. I've tried to work out a solution, but without success. I've tried 'advance :: DA -> State -> String -> State advance (start, step, accept) State Char:Chars = advance (start, step, accept) (step State Char) Chars ' I aimed to implement a recursive functions to cycle through the elements of the String to be read. Loading it into GHCi produces a parse error. So where is my mistake?
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    2. CO@user1838559: Variables have to begin with a lower case letter, so use `chars` not `Chars`. Also, operators like `:` have lower precedence than function application, even in patterns, so you need to put parentheses around `(char:chars)`.
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    3. CO@hammer: Thank You for that answer. I apologize for asking such a stupid question and for wasting your time with these spelling-mistakes ;-)
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