F＃整数文件指令

Question

I've been using fslex and fsyacc, and the F# source files ( .fs they generate from the lexer ( .fsl ) and parser ( .fsp ) rules refer to the original .fsl (and sometimes to the same .fs source file) all over the place with statement such as this (numbers are line numbers):

lex.fs
1      # 1 "/[PROJECT-PATH-HERE]/lex.fsp
...
16     # 16 "/PROJECT-PATH-HERE]/lex.fs
17     // This is the type of tokens accepted by the parser
18     type token =
19       | EOF
...

Also, the .fs files generated by pars.fsp do the same kind of thing, but additionaly reference to the F# signature file ( .fsi ) generated alongside it. What does any of this do/mean?

Answer 1

The annotations you see in the generated code are F# Compiler Directives (specifically, the 'line' directive).

The 'line' directive makes it so that when the F# compiler needs to emit a warning/error message for some part of the generated code, it has a way to determine which part of the original file corresponds to that part of the generated code. In other words, the F# compiler can generate a warning/error message referencing the original code which is the basis of the generated code causing the error.