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Last update Thu Mar 6 15:45:43 2008

# std.functional

Functions that manipulate other functions.
Author:
Andrei Alexandrescu

template unaryFun(string comp,bool byRef = false)
  Transforms a string representing an expression into a unary function. The string must use symbol name a as the parameter.
  Example:

      alias unaryFun!("(a & 1) == 0") isEven;
      assert(isEven(2) && !isEven(1));

template binaryFun(string comp)
  Transforms a string representing an expression into a Boolean binary predicate. The string must use symbol names a and b as the compared elements.
  Example:

      alias binaryFun!("a < b") less;
      assert(less(1, 2) && !less(2, 1));
      alias binaryFun!("a > b") greater;
      assert(!greater("1", "2") && greater("2", "1"));

template adjoin(F...)
  Takes multiple functions and adjoins them together. The result is a std.typecons.Tuple with one element per passed-in function. Upon invocation, the returned tuple is the adjoined results of all functions.
  Example:

      static bool f1(int a) { return a != 0; }
      static int f2(int a) { return a / 2; }
      auto x = adjoin!(f1, f2)(5);
      assert(is(typeof(x) == Tuple!(bool, int)));
      assert(x._0 == true && x._1 == 2);

template compose(alias F1,alias F2)
template compose(alias F1,string F2)
template compose(string F1,alias F2)
template compose(string F1,string F2)
  Composes two functions F1 and F2, returning a function F(x) that in turn returns F1(F2(x)).
  Example:

      auto x = 5;
      auto y = compose!("!a", "a > 0")(x);
      assert(!y);

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