Editing Unlambda (section)

==Version 2 built-in functions==
More built-ins were introduced in Unlambda version 2. [[Input/output|Input]] is facilitated by operators <code>@</code> and <code>?''u''</code>. When <code>@</code> is applied to a function ''x'', a character is read from input, and stored as the "current character"; then ''x'' is applied to <code>i</code>. However, if no more characters were available on input, the ''current character'' is left undefined, and ''x'' is applied to <code>v</code> instead. When a function <code>?''u''</code> is applied to a function ''x'', the result is the evaluation of <code>`''x''i</code> if the current character is ''u'', otherwise <code>`''x''v</code> is evaluated.

There is also a "reprint" operator <code>|</code>. When <code>`|''x''</code> is evaluated, the function ''x'' is applied to <code>.''u''</code> if ''u'' is the current character, or to <code>v</code> if there is no current character.

Finally, there is an exit operator <code>e</code>. When <code>e</code> is applied to ''x'', the execution of the program is terminated, and ''x'' is taken as the result of the program (most of the currently existing interpreters ignore the result anyway).