rfc:ast_based_parsing_compilation_process
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rfc:ast_based_parsing_compilation_process [2012/09/07 13:15] – nikic | rfc:ast_based_parsing_compilation_process [2017/09/22 13:28] (current) – external edit 127.0.0.1 | ||
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- | ====== Request for Comments: Moving to an AST-based parsing/ | + | ====== Request for Comments: Moving to an AST-based parsing/ |
* Date: 2012-09-04 | * Date: 2012-09-04 | ||
* Author: Nikita Popov < | * Author: Nikita Popov < | ||
- | * Status: | + | * Status: |
+ | * [[http:// | ||
+ | * Superseded by: [[rfc: | ||
===== Introduction ===== | ===== Introduction ===== | ||
+ | |||
+ | **Note: This RFC has been superseded by another [[rfc: | ||
Currently PHP uses a single-pass compilation process, i.e. the parser directly invokes opcode compilation routines. Most other languages on the other hand use an intermediary structure to separate those two phases: The parser only emits an abstract syntax tree (AST), which is then used by a separate compiler to emit instructions. The use of an AST decouples the two phases and as such allows for greater flexibility and deeper analysis. | Currently PHP uses a single-pass compilation process, i.e. the parser directly invokes opcode compilation routines. Most other languages on the other hand use an intermediary structure to separate those two phases: The parser only emits an abstract syntax tree (AST), which is then used by a separate compiler to emit instructions. The use of an AST decouples the two phases and as such allows for greater flexibility and deeper analysis. | ||
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==== Elimination of various quirks ==== | ==== Elimination of various quirks ==== | ||
- | Currently there is various quirks in the emitted opcodes which can be attributed to the use of a single-pass compiler. Some examples: | + | Currently there are various quirks in the emitted opcodes which can be attributed to the use of a single-pass compiler. Some examples: |
* The NOP opcodes that are inserted in several places. (Yes, this point isn't particularly important) | * The NOP opcodes that are inserted in several places. (Yes, this point isn't particularly important) | ||
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With the current single-pass compiler some things are very hard / near impossible to implement. This actively influences syntax decisions. | With the current single-pass compiler some things are very hard / near impossible to implement. This actively influences syntax decisions. | ||
- | Two examples of syntax that is currently not possible, but would be possible with a syntax tree: | + | A few examples of syntax that is currently not possible, but would be possible with a syntax tree: |
* Array destructuring using something like '' | * Array destructuring using something like '' | ||
* List comprehensions / generator expressions where the result expression comes first, e.g. '' | * List comprehensions / generator expressions where the result expression comes first, e.g. '' | ||
+ | * C#-style expression trees (which form the basis for LINQ) | ||
+ | |||
+ | Apart from larger syntax limitations the current system commonly also affects smaller syntax decisions. One example here are the strange parentheses requirements for the '' | ||
+ | |||
+ | ==== Better error messages ==== | ||
- | Apart from larger syntax limitations | + | Currently many things are directly enforced in the grammar which should really be checked during compilation (or a completely separate pass). E.g. if you try to initialize a class property with a non-static value, you'll get a rather unintelligible parse error message, instead of something like '' |
===== Disadvantages ===== | ===== Disadvantages ===== |
rfc/ast_based_parsing_compilation_process.txt · Last modified: 2017/09/22 13:28 by 127.0.0.1