rfc:ast_based_parsing_compilation_process

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rfc:ast_based_parsing_compilation_process [2012/09/04 19:41] – created nikicrfc:ast_based_parsing_compilation_process [2012/09/04 19:49] – nikic
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 A more interesting example is the fact that whenever you access a static member like ''Foo::$bar'' an unused compiled-variable for ''$bar'' is emitted. The compiler thinks that ''$bar'' is a normal variable and as such creates an A more interesting example is the fact that whenever you access a static member like ''Foo::$bar'' an unused compiled-variable for ''$bar'' is emitted. The compiler thinks that ''$bar'' is a normal variable and as such creates an
-unnecessary and unused CV for it.+unnecessary CV for it.
  
 Other quirks (which actually influences the behavior) is caused by the separation of ''variable'' and ''expr_without_variable'' in the grammar. For example parentheses may cause subtle changes in behavior (''func($foo)'' Other quirks (which actually influences the behavior) is caused by the separation of ''variable'' and ''expr_without_variable'' in the grammar. For example parentheses may cause subtle changes in behavior (''func($foo)''
-and ''func(($foo))'' have different behavior).+and ''%%func(($foo))%%'' have different behavior).
  
 All these can be eliminated when an AST is used. All these can be eliminated when an AST is used.
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 One example of syntax that is currently impossible is array destructuring without a special ''list()'' construct. The syntax ''[$a, $b] = [$b, $a]'' that is common in other languages is not possible to implement in PHP due to parser limitations. One example of syntax that is currently impossible is array destructuring without a special ''list()'' construct. The syntax ''[$a, $b] = [$b, $a]'' that is common in other languages is not possible to implement in PHP due to parser limitations.
  
-Another example are list comprehensions / generator expressions where the result expression comes first (e.g. ''[x * x for x in list]'' in Python). In PHP only the reversed syntax is possible (''foreach ($list as $x) yield $x * $x'').+Another example are list comprehensions / generator expressions where the result expression comes first (e.g. ''[x * x for x in list]'' in Python). In PHP only the reversed syntax is possible (''[foreach ($list as $x) yield $x * $x]'').
  
 Those are two examples of larger limitations, but smaller syntax decisions are often driven by parser limitations too. An AST allows implementing many syntax elements that would otherwise be impossible. (One of the main reasons for this is that an AST based parser does not require mid-rule semantic action reduction.) Those are two examples of larger limitations, but smaller syntax decisions are often driven by parser limitations too. An AST allows implementing many syntax elements that would otherwise be impossible. (One of the main reasons for this is that an AST based parser does not require mid-rule semantic action reduction.)
rfc/ast_based_parsing_compilation_process.txt · Last modified: 2017/09/22 13:28 by 127.0.0.1

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