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postscript [2020/02/20 17:43] christian [exception handling example] |
postscript [2020/02/23 15:53] (current) christian [Get the code] |
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===== Get the code ===== | ===== Get the code ===== | ||
- | Load the package | + | Load the packages **[Values]** and **[PostScript]** from the [[storeaccess|Cincom Public Store]] into your [[http:// |
- | Tests are in package **[PostScript Testing]**. | + | Tests are in package **[PostScript Testing]**. The package can be used stand-alone without PDFtalk. It only depends on the **[Values]** package. |
- | The bundle | + | The package is now part of the **{PDFtalk}** |
===== Use it ===== | ===== Use it ===== | ||
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Ultimately I want to extract text from PDFs for which I need CMaps. | Ultimately I want to extract text from PDFs for which I need CMaps. | ||
- | Also, I like PostScript. I used it quite a bit to write UIs with Display PostScript on a Sun Solaris | + | Also, I like PostScript. I used it quite a bit to write UIs with Display PostScript on a Sun NeWS(([[https:// |
===== PostScript programming introduction ===== | ===== PostScript programming introduction ===== | ||
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</ | </ | ||
leaves 49 on the stack. | leaves 49 on the stack. | ||
- | |||
At the start of a PostScript interpreter, | At the start of a PostScript interpreter, | ||
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* **global dict** " | * **global dict** " | ||
* **system dict** " | * **system dict** " | ||
+ | |||
+ | New definitions are put into the topmost dictionary of the stack. This allows programs to override system definitions. The NeWS system from Sun used this to implement an object oriented Display PostScript with the dictionaries as classes. Another view is to see the dictionaries as namespaces. | ||
+ | |||
+ | The dictionaries can be named with an interesting trick: the dictionary itself is stored under a key which is interpreted as its name. The system dict for example is constructed like: | ||
+ | <code smalltalk> | ||
+ | | dict | | ||
+ | dict := PSDictionary new. | ||
+ | dict at: #systemdict put: dict. | ||
+ | ^dict | ||
+ | </ | ||
+ | |||
+ | This creates a recursive structure which is not handled well by the standard Smalltalk dictionary, hence '' | ||
+ | |||
+ | Interestingly, | ||
+ | Including the naming scheme for dictionaries! | ||
(more will be written on demand...) | (more will be written on demand...) | ||
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</ | </ | ||
+ | I think that both approaches are very elegant. | ||