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Eli: Translator Construction Made Easy

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Pattern-based Text Generator

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Output Functions

PTG separates the composition of a target text from outputting it: A target text is composed by calls of pattern functions. They yield results of type PTGNode representing the target text or fragments thereof.

There are three predefined PTG functions that can be applied to PTGNode values in order to output the text. They have the following signatures: 

   PTGNode PTGOut(PTGNode r)
   PTGNode PTGOutFile(char *f, PTGNode r)
   PTGNode PTGOutFPtr(FILE *f, PTGNode r)

A call PTGOut (x) writes the text represented by x to stdout.

The function PTGOutFile takes the name of the output file as an additional parameter. A call PTGOutFile (n, x) opens the file named n for writing, writes the text represented by x to it, and closes the file before returning.

The function PTGOutFPtr takes the file pointer to an already open file as additional parameter. A call PTGOutFPtr (f, x) writes the text represented by x to f, and leaves The function PTGOutFPtr takes open upon exit.

Each of the functions yields its PTGNode argument as result. Hence, nested calls of output functions may produce parts of the complete target text on separate files, e.g. 

   PTGOutFile ("f1",
      PTGModule (
         PTGOutFile ("f2", PTGInterface ( ...... )),
         PTGBody ( .... )))
In the above example a Module is composed by two text fragments Interface and Body. The whole text is written to the file f1. The Interface fragment is also written to the file f2.

Of course nested calls like the above can be decomposed by storing intermediate PTGNode values. Nested calls of PTGOutFile to the same file would destroy the results of the former calls. Nested calls of PTGOutFPtr to the same file would append the results of each call to the end of the file.

Note: Be aware that the output functions do not add a newline character to the end of an output text. It has to be explicitly specified by a pattern. This behavior has been changed compared to previous versions of PTG. Adding a newline character to a text is simply specified by a pattern like 

     NewLine:    $ "\n"

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