Parsing in Segments

Pass#1 is responsible for so many things it needs to be designed very carefully. I have come up with a plan about the remaining compiling phases: There will be 3 or 4 passes in total of which Pass#1 is the parser. Its main job is to compile the symbol table for the source code, and generate variances of the generic classes and functions. In short, it will prepare the source code for Pass#2 where the actual compilation of each procedure takes place. Of course, this involves making the code as clean as possible by removing modifiers and certain other structural “particles”.

Parsing in general can be quite difficult a task, but this time I’ve taken entirely different approach. As we begin Pass#1 (for each line separately) some basic syntax checks have already been done. Therefore we can safely assume that the line always begins with:

• Pointer literal
• Identifier
• Label
• Full-line special data segment
• Keyword

Each of which launches a mini-parser of their own. These include ParseKeywords(), ParseStatementValue(), ParseAssignment(), ParseParamList(), ParseDeclaration() and ParseModifiers(). They scan the terminals of the current line by segments, i.e group terminals based on which class they belong to. All this is done recursively so in case of a failure, the entire call stack rolls back, ultimately terminating the entire compiling process. The pros of the recursive parsing is that it allows a flexible identification of expressions which belong to a multi-part statement such as the For-statement.

In addition, all in-built statements have their own parsers that make sure the keyword has been used within a proper declaration context, and that those statements that define a code block, follow a valid hierarchical structure. As many syntax checks will be made as possible, but the final compilation in Pass#2 will detect the rest of them.

CoolBasic V3 follows very sophisticated and strict syntactical rules similar to VB.NET. This means that in order to parse a simple Break-statement I must first establish the base for parsing modifiers, Modules, Functions, and Repeat…Until. In another words, I must first set up alot of functions just to get things running by putting it all together for the minimum. Lots of code is required before I can even run the basic tests (for example scope list and the symbol table). Pass#1 is coming along nicely, though.