Reusing the internals
lazarus / 64-FPC development

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int-index · 2015-02-01 21:44

I am developing a translator from Pascal to Haskell (source here:
https://github.com/int-index/sodium) and instead of reimplementing a
parser and a typechecker for Pascal, I would really like to reuse the
ones in FPC. So I need to modify FPC somehow to make it emit parsed
type-annotated version of source code in some easy to parse format
(such as XML).

Basically the idea is to get from this:
Code: [Select]var x: Integer; begin x := ...; WriteLn(x); end;to
something like this:
Code: [Select]<source>
       <variables>
              <variable name="x" type="Integer"></variable>
       </variables>
       <body>
              <assignment>
                     <lhs><variable name="x"></variable></lhs>
                     <rhs>...</rhs>
              </assignment>
              <procedure-call name="WriteLn">
                     <argument>
                       <function-call special="Integer-to-String">
                           <variable-access name="x"></variable-
access>
                       </function-call>
                     </argument>
              </procedure-call>
          </body>
   </source>
Note the added type-conversion (reusing FPC typechecker and semantic
analysis).

My questions are: is this possible? Is it difficult? Where do I start
if I want to implement it?

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Blaazen · 2015-02-01 22:23

Maybe you should ask on FPC-Pascal or FPC-Devel mailing list, you have
better chance to meet freepascal developers there.

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engkin · 2015-02-02 00:28

Take a look here. It advices using fcl-passrc and the example
test_parser in packages\fcl-passrc\examples.

One more thing: WriteLn is not a real procedure call. The compiler
generates suitable set of calls based on the number and types of
parameters passed to WriteLn.

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JuhaManninen · 2015-02-02 06:19

Quote from: int-index on February 01, 2015, 10:44:45 pmI am developing
a translator from Pascal to Haskell

Heh, what will you do with Pascal variables and loops?
Anyway, good luck!

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Leledumbo · 2015-02-02 06:44

Quote from: int-index on February 01, 2015, 10:44:45 pmis this
possible?
certainly
Quote from: int-index on February 01, 2015, 10:44:45 pmIs it
difficult?
depending on your knowledge and skill
Quote from: int-index on February 01, 2015, 10:44:45 pmWhere do I
start if I want to implement it?
fpc -vp <your program or unit> produces tree.log in a LISP-like
notation, though I'm afraid not enough for your approach for the
purpose. Using fcl-passrc classes and extending them with appropriate
backend for XML/Haskell (whatever you want) as engkin said will be a
better one.