package ppx_here

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Expands [%here] into its location

Install

Dune Dependency

Authors

Maintainers

Sources

ppx_here-v0.10.0.tar.gz
sha256=26d56823ea946a5808466b9eed638a83b855323e03a03fdd7c964249758e488b
md5=19333d8afcac45269769560645b3fa1f

README.md.html

ppx_here

A ppx rewriter that defines an extension node whose value is its source position.

Syntax

ppx_here rewrites the extension [%here] in expressions, by replacing it by a value of type Source_code_position.t (i.e. Lexing.position) corresponding to the current position. It respects line number directives.

For instance:

let _ =
  print_endline [%here].Lexing.pos_fname

becomes:

let _ =
  print_endline
    {
      Lexing.pos_fname = ppx/ppx_here/test/test.ml";
      pos_lnum = 2;
      pos_cnum = 26;
      pos_bol = 8;
    }.Lexing.pos_fname

Usage

This is normally used so exceptions can contain better positions. An example is Core_kernel.Std.Option.value_exn, which takes an optional position so that if you have a stack trace, you can get still the origin of the exception.

It can also be used in cases where stack traces are useless (for instance in monads with a complicated control flow).

Command line flag

If the flag -dirname <dir> is given, relative filenames are made relative to <dir>. <dir> can be a relative path.

<dir> can be chosen as the path from the root of the repository to the directory of the source, to make filenames unique within the repository (which avoids ambiguities as there can be many files called server.ml, common.ml or config.ml).

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