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Often it's OK to directly translate a language construct (like an if statement) to a lightly-parametrized code template, not unlike an HTML template.Īgain, ignore efficiency and concentrate on correctness. Trivial cases are as indispensable at troubleshooting as smart and complex. For instance, this step will make sure that the number of parameters passed to a function from another module is correct.Īgain, write and run a lot of test cases. The validator will also resolve references to other modules written in your language, load these other modules and use in the validation process. The validator will detect such errors looking at the tree. An example is a duplicate declaration of the same variable or passing a parameter of a wrong type. Most probably your language allows for syntactically correct constructions that may make no sense in certain contexts. There are plenty of simple ways to dump a tree to a file and to quickly load it back. If your language has modules, the output of the parser may be the simplest representation of 'object code' you generate. Output of your parser is an abstract syntax tree. Write a lot of test cases, both positive and negative reuse the code you wrote while defining the language.
The parser should detect and report syntax errors. You may also write your own parser from scratch, but it only worth it if syntax of your language is dead simple. It would be a shame to end up with an ill-defined language that cannot accept valid code. Concentrate on 'positive' tests that accept correct code, as opposed to detection of incorrect code. Get well-acquainted with your preferred testing framework. Your entire language should be covered by test cases effectively it will be defined by them. It's also OK to write different stages of a compiler in different languages, if needed. It only needs to be correct enough and easy to modify. The first version does not have to be fast, or efficient, or feature-complete. Use simple algorithms you understand well. It's totally OK to write a compiler in Python or Ruby or whatever language is easy for you. It's high time to write snippets of code in your new language as test cases for the future compiler. Use whatever notation you want, but make sure you have a complete and consistent description of your language. These things is the stuff programs are made of on the logical level. Make sure you're comfortable working with graphs, especially trees. If this stuff is too hard for you right now, read some intros on parsing first usually parsing libraries include intros and examples. This is classic and is still quite applicable today. Create the simplest thing that could possibly work.
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This classic sequence applies to all software development, but bears repetition.Ĭoncentrate on the first step of the sequence. In languages like Java and C# linking may be totally dynamic, done by the VM at load time.
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Most native-code compilers know how to call a linker to produce an executable, but it's not a compilation step per se.
the use of vector instructions when possible, instruction reordering to increase branch prediction efficiency, and so on.Īfter that, object code is ready for linking. Then that language is converted into platform-specific code (x86, ARM, etc) doing roughly the same thing in a platform-optimized way. They use an intermediate low-level but platform-independent language for initial code generation. Most modern compilers (for instance, gcc and clang) repeat the last two steps once more. Peephole optimization: the low-level code is scanned for simple local inefficiencies which are eliminated.Some function calls can be inlined at this stage, some loops unrolled, etc. Code generation: the AST is transformed into linear low-level code, with jumps, register allocation and the like.early calculation of common subexpressions and constant expressions, eliminating excessive local assignments (see also SSA), etc. Equivalent transformations and high-level optimization: the AST is transformed to represent a more efficient computation with the same semantics.unreachable code or duplicate declarations. Semantic validation: weeding out syntactically correct statements that make no sense, e.g.Resolution of references to other modules (C postpones this step till linking).Parsing: the source text is converted to an abstract syntax tree (AST).A typical compiler does the following steps:
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