3 ms·

FYI: Parsing and compiling in the programming language sense are orthogonal problems. Both are major challenges in cpp compilers.

blenderob 1y ago
> FYI: Parsing and compiling in the programming language sense are orthogonal problems. How so? In Ada, Fortran, C, C++, Java, Python, etc. parsing is one of the many phases of compiling. Far from being orthogonal problems, parsing is a sub-problem of compiling.
- Pet_Ant 1y ago
  The amount of time being consumed by parsing is vanishingly small. It's a lot like the decoding time spent on x86 code is marginal nowadays compared to the speculative and reordering logic. YACC was called "Yet Another Compiler Compiler" because back in the day parsing was the bulk of compilation, now it's relatively minimal.
- vkazanov 1y ago
  Parsing is almost always a part of a programming language compiler but it doesn't have to be. When we parse a string, we go up from low-level human-readable strings to intermediate parse trees to a high-level AST. A process of compilation goes down from some kind of a high-level internal representation through phases to something that is close to the target low-level language. It can go down from an AST, or LLVM-s internal representation, or whatever. Problems solved by both processes are different: 1. Parsing is about finding string patterns (using regexps or PEGs or whatever) and representing these using a more strict high-level structure. The structure is usually tree-like but is also often a graph. 2. Compiling takes something high-level (a tree, a graph, etc) and emits something different, usually simplified. A good example is a typical lisp implementation where the parser is trivial but compilation phases represent numerous simplifying phases.
thaumasiotes 1y ago
What I've read is that C++'s biggest compiling problem is specifically that the language is difficult to parse. You can't compile without parsing, so no, they're not orthogonal problems. Compiling is a parsing step followed by an emission step. (And just to be completely clear, I'm not saying that the difficulty of parsing C++ makes it miserable to write a compiler. I'm saying that the difficulty of parsing C++ makes it miserable to run a compiler.)

blenderob 1y ago

> FYI: Parsing and compiling in the programming language sense are orthogonal problems. How so? In Ada, Fortran, C, C++, Java, Python, etc. parsing is one of the many phases of compiling. Far from being orthogonal problems, parsing is a sub-problem of compiling.

Pet_Ant 1y ago
The amount of time being consumed by parsing is vanishingly small. It's a lot like the decoding time spent on x86 code is marginal nowadays compared to the speculative and reordering logic. YACC was called "Yet Another Compiler Compiler" because back in the day parsing was the bulk of compilation, now it's relatively minimal.
vkazanov 1y ago
Parsing is almost always a part of a programming language compiler but it doesn't have to be. When we parse a string, we go up from low-level human-readable strings to intermediate parse trees to a high-level AST. A process of compilation goes down from some kind of a high-level internal representation through phases to something that is close to the target low-level language. It can go down from an AST, or LLVM-s internal representation, or whatever. Problems solved by both processes are different: 1. Parsing is about finding string patterns (using regexps or PEGs or whatever) and representing these using a more strict high-level structure. The structure is usually tree-like but is also often a graph. 2. Compiling takes something high-level (a tree, a graph, etc) and emits something different, usually simplified. A good example is a typical lisp implementation where the parser is trivial but compilation phases represent numerous simplifying phases.

thaumasiotes 1y ago

What I've read is that C++'s biggest compiling problem is specifically that the language is difficult to parse. You can't compile without parsing, so no, they're not orthogonal problems. Compiling is a parsing step followed by an emission step. (And just to be completely clear, I'm not saying that the difficulty of parsing C++ makes it miserable to write a compiler. I'm saying that the difficulty of parsing C++ makes it miserable to run a compiler.)