diff options
Diffstat (limited to 'flang/docs/C++17.md')
| -rw-r--r-- | flang/docs/C++17.md | 16 |
1 files changed, 8 insertions, 8 deletions
diff --git a/flang/docs/C++17.md b/flang/docs/C++17.md index f36110a..9137827 100644 --- a/flang/docs/C++17.md +++ b/flang/docs/C++17.md @@ -6,7 +6,7 @@ --> -# C++14/17 features used in f18 +# C++14/17 features used in Flang ```{contents} --- @@ -27,7 +27,7 @@ out the details of how our C++ code should look and gives guidance about feature usage. We have chosen to use some features of the recent C++17 -language standard in f18. +language standard in Flang. The most important of these are: * sum types (discriminated unions) in the form of `std::variant` * `using` template parameter packs @@ -41,7 +41,7 @@ in this list because it's not particularly well known.) ## Sum types First, some background information to explain the need for sum types -in f18. +in Flang. Fortran is notoriously problematic to lex and parse, as tokenization depends on the state of the partial parse; @@ -57,7 +57,7 @@ a unified lexer/parser. We have chosen to do so because it is simpler and should reduce both initial bugs and long-term maintenance. -Specifically, f18's parser uses the technique of recursive descent with +Specifically, Flang's parser uses the technique of recursive descent with backtracking. It is constructed as the incremental composition of pure parsing functions that each, when given a context (location in the input stream plus some state), @@ -73,7 +73,7 @@ of Fortran. The specification of Fortran uses a form of BNF with alternatives, optional elements, sequences, and lists. Each of these constructs -in the Fortran grammar maps directly in the f18 parser to both +in the Fortran grammar maps directly in Flang's parser to both the means of combining other parsers as alternatives, &c., and to the declarations of the parse tree data structures that represent the results of successful parses. @@ -87,10 +87,10 @@ The bounded polymorphism supplied by the C++17 `std::variant` fits those needs exactly. For example, production R502 in Fortran defines the top-level program unit of Fortran as being a function, subroutine, module, &c. -The `struct ProgramUnit` in the f18 parse tree header file +`struct ProgramUnit` in the Flang parse tree header file represents each program unit with a member that is a `std::variant` over the six possibilities. -Similarly, the parser for that type in the f18 grammar has six alternatives, +Similarly, the parser for that type in Flang's grammar has six alternatives, each of which constructs an instance of `ProgramUnit` upon the result of parsing a `Module`, `FunctionSubprogram`, and so on. @@ -99,7 +99,7 @@ parse is typically implemented with overloaded functions. A function instantiated on `ProgramUnit` will use `std::visit` to identify the right alternative and perform the right actions. The call to `std::visit` must pass a visitor that can handle all -of the possibilities, and f18 will fail to build if one is missing. +of the possibilities, and Flang will fail to build if one is missing. Were we unable to use `std::variant` directly, we would likely have chosen to implement a local `SumType` replacement; in the |