Development of the Compiler

Architecture of the Compiler

ANTLR

• the grammar is in openpearl/compliter/src/SmallPearl.g4
• ANTLR generates a lexer and parser in JAVA using the visitor-pattern
• The major steps in the compiler are
  • syntactical analysis is done by ANTLR-code with currently no further informations. It would be good to improve the error messages!
  • after the syntactical analysis, ANTLR provides an abstract syntax tree (AST) for the application program
  • the AST ist traversed several times
    1. setup the symbol table
    2. evaluate the types of expressions
    3. run the semantical analysis in servreal passes
  • if all passes were ok, the CppCodeGenerator creates C++ code from the AST and additional information

Additional Infomations during Compilation

• each node of the AST is is identified by a context (type ParserRuleContext)
• the AST should not be modified to allow reordering of the analysis passes
• there is an infrastructur of extensible ASTAttributes, which contain information of e.g. references to the symbol table, type of expressions, ..
• the symbol table is hierarchically organiszedand knows the location of the definition of the symbol, its type,...

Coding Conventions

• Java conding conventions should be used
• indenting should be according google style
  • with 4 spaces instead of 2
  • Eclipse users may use the setting eclipse-openpearl-style.xml
• documentation should be done with Javadoc at level of classes as a minimum, further comments are appreciated

Error treatment

• The error treatment started in the beginning with exception throwing
• Since 2019, an ErrorStack class exists, which provides more informative error messages for the application engineers
• The migration toward the ErrorStack is ongoing

Testing

Annotations

Since march 2021 we have a mechanism to check if illegal PEARL code produces expected error-, warning- and note-messages.

Example:

 DCL x FIXED INIT(1.2);
 /*$              ^
 error: initializer must be of type FIXED -- but is of type FLOAT
 */

• An annotation is placed in the next line aftre the source line, which the compiler should complain
• the annotationm is marked as a multiline pearl comment with the starting tag /*$
• the annotation starts at the beginning iof the line
• a circimflex ^ marks the column position for the error message; if the markre is in column 1-3, the circumflex must be in the next line
• the next line contains the error message. Spaces at the end will be ignored
• the annotation is closed with */ - and nothing else in this line
• multiple annotations for a source line appear in a compact sequence

The test script runs in openpearl/testsuite/verifyAnnotation/.
It checks alle files with exteniosn .prl in this folder and sub-folders. Possible errors in first step of processing
* source file contains no annotation
* malformed annotation

Possible errors in second pass of processing
* annotation did not match an error message in position
* annotation differs in text
* annotation was not matched by a compiler error
* unexpected compiler error

The organisation of the tests is not defined, yet. Proposals are wellcome