90:, though lexical (static) scoping is far more common. In lexical scoping (or lexical scope; also called static scoping or static scope), if a variable name's scope is a certain block, then its scope is the program text of the block definition: within that block's text, the variable name exists, and is bound to the variable's value, but outside that block's text, the variable name does not exist. By contrast, in dynamic scoping (or dynamic scope), if a variable name's scope is a certain block, then its scope is that block and all functions transitively called by that block (except when overridden again by another declaration); after the block ends, the variable name does not exist. Some languages, like
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value to a global (package) variable, which lasts until the end of the enclosing block. However, the variable is visible to any function called from within the block. To create lexically-scoped local variables, use the
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98:, allow the programmer to choose static or dynamic scoping when defining or redefining a variable. Examples of languages that use dynamic scoping include
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semantics allow the parameters to act as aliases of the values passed as arguments, allowing the subroutine to modify variables outside its own scope.
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as a language was inspired also by Perl, but in this case, the notation was made simpler: a global variable name must be preceded by a $ sign, like
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passed to it. In most languages, these local parameters are treated the same as other local variables within the subroutine. In contrast,
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calls itself, local variables in each instance of the function are given distinct
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semantics provide a called subroutine with its own local copy of the
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This happens since the global variable $ a is modified to a new
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Conrad Irwin. "LSpace: Dynamic scope for Ruby". December 2012
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variable would be limited to the static scope of the function
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isn't what most people think of as “local”.". Instead, the
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Static locals in global functions have the same lifetime as
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would have printed 1 three times since in that case the
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To understand how it works consider the following code:
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is available in many mainstream languages (including
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