Return type: The same as the type of its argument
Returns:       

The value of the expression

  ~ expression

You can use the identity operator (~) to force an expression contained in a pattern to be evaluated so that the result of the expression becomes part of the pattern. This is only necessary for expressions which are ambiguous in their syntax, so that OmniMark cannot tell, without the identity operator, whether the expression is a value expression to be evaluated or a sequence of pattern expressions.

The identity operator is required in the following cases:

• variable names, with or without shelf indexers
• switch literals (true and false).
• infix function calls

You must use the identity operator when using an item on a shelf in a pattern:

  ~foo[2]
  ~foo{"bar"}

You must use the identity operator when calling an infix function (one in which the function name is placed between its arguments):

  ~("d" % foo)
  ~(foo take (any** ","))

You can also use the identity operator in place of the keyword when to add a conditional expression to a pattern. Thus you can replace:

  (when title="")

  ~(title="")

Related Concepts    Pattern matching

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