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Category:Fexl: Difference between revisions
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A symbol may be defined within a Fexl program, or its definition may be left entirely open. The definitions of all open symbols are supplied by a ''context''. A context is a function which supplies definitions for symbols. A context function is itself written in Fexl.
A Fexl program may therefore be resolved inside an arbitrary context, giving whatever meanings you like to all its open symbols. This makes it easy to wrap a Fexl program in an enhanced or restricted context. For example, in a web context you probably don't want "delete_file" to be defined at all, at least not in its normal sense. So
Ultimately the core functions of Fexl are written in the [[C]] programming language. To write a new core function named "X" within Fexl, you simply create an appropriate C routine named "fexl_X". It automatically becomes available as a built-in Fexl function.
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