# Module Misc

    module Misc: sig .. end

Miscellaneous useful types and functions

Warning: this module is unstable and part of compiler-libs.

## Reporting fatal errors

    val fatal_error : string -> 'a

Raise the `Fatal_error` exception with the given string.

    val fatal_errorf : ('a, Format.formatter, unit, 'b) format4 -> 'a

Format the arguments according to the given format string and raise `Fatal_error` with the resulting string.

    exception Fatal_error

## Exceptions and finalization

    val try_finally : ?always:(unit -> unit) -> ?exceptionally:(unit -> unit) -> (unit -> 'a) -> 'a

`try_finally work ~always ~exceptionally` is designed to run code in `work` that may fail with an exception, and has two kind of cleanup routines: `always`, that must be run after any execution of the function (typically, freeing system resources), and `exceptionally`, that should be run only if `work` or `always` failed with an exception (typically, undoing user-visible state changes that would only make sense if the function completes correctly). For example:

          let objfile = outputprefix ^ ".cmo" in
          let oc = open_out_bin objfile in
          Misc.try_finally
            (fun () ->
               bytecode
               ++ Timings.(accumulate_time (Generate sourcefile))
                   (Emitcode.to_file oc modulename objfile);
               Warnings.check_fatal ())
            ~always:(fun () -> close_out oc)
            ~exceptionally:(fun _exn -> remove_file objfile);

If `exceptionally` fail with an exception, it is propagated as usual.

If `always` or `exceptionally` use exceptions internally for control-flow but do not raise, then `try_finally` is careful to preserve any exception backtrace coming from `work` or `always` for easier debugging.

    val reraise_preserving_backtrace : exn -> (unit -> unit) -> 'a

`reraise_preserving_backtrace e f` is (f (); raise e) except that the current backtrace is preserved, even if `f` uses exceptions internally.

## List operations

    val map_end : ('a -> 'b) -> 'a list -> 'b list -> 'b list

`map_end f l t` is `map f l @ t`, just more efficient.

    val rev_map_end : ('a -> 'b) -> 'a list -> 'b list -> 'b list

`map_end f l t` is `map f (rev l) @ t`, just more efficient.

    val map_left_right : ('a -> 'b) -> 'a list -> 'b list

Like `List.map`, with guaranteed left-to-right evaluation order

    val for_all2 : ('a -> 'b -> bool) -> 'a list -> 'b list -> bool

Same as `List.for_all` but for a binary predicate. In addition, this `for_all2` never fails: given two lists with different lengths, it returns false.

    val replicate_list : 'a -> int -> 'a list

`replicate_list elem n` is the list with `n` elements all identical to `elem`.

    val list_remove : 'a -> 'a list -> 'a list

`list_remove x l` returns a copy of `l` with the first element equal to `x` removed.

    val split_last : 'a list -> 'a list * 'a

Return the last element and the other elements of the given list.

    val repeated_label : (string option * 'a) list -> string option

Detects a repeated label - for use with labeled tuples.

## Hash table operations

    val create_hashtable : int -> ('a * 'b) list -> ('a, 'b) Hashtbl.t

Create a hashtable with the given initial size and fills it with the given bindings.

## Extensions to the standard library

    module Stdlib: sig .. end

## Operations on files and file paths

    val find_in_path : string list -> string -> string

Search a file in a list of directories.

    val find_in_path_rel : string list -> string -> string

Search a relative file in a list of directories.

    val normalized_unit_filename : string -> (string, string) Result.t

Normalize file name `Foo.ml` to `foo.ml`, using NFC and case-folding. Return `Error` if the input is not a valid utf-8 byte sequence

    val find_in_path_normalized : string list -> string -> string

Same as `Misc.find_in_path_rel` , but search also for normalized unit filename, i.e. if name is `Foo.ml`, allow `/path/Foo.ml` and `/path/foo.ml` to match.

    val remove_file : string -> unit

Delete the given file if it exists and is a regular file. Does nothing for other kinds of files. Never raises an error.

    val expand_directory : string -> string -> string

`expand_directory alt file` eventually expands a `+` at the beginning of file into `alt` (an alternate root directory)

    val split_path_contents : ?sep:char -> string -> string list

`split_path_contents ?sep s` interprets `s` as the value of a "PATH"-like variable and returns the corresponding list of directories. `s` is split using the platform-specific delimiter, or `~sep` if it is passed.

Returns the empty list if `s` is empty.

    val copy_file : in_channel -> out_channel -> unit

`copy_file ic oc` reads the contents of file `ic` and copies them to `oc`. It stops when encountering EOF on `ic`.

    val copy_file_chunk : in_channel -> out_channel -> int -> unit

`copy_file_chunk ic oc n` reads `n` bytes from `ic` and copies them to `oc`. It raises `End_of_file` when encountering EOF on `ic`.

    val string_of_file : in_channel -> string

`string_of_file ic` reads the contents of file `ic` and copies them to a string. It stops when encountering EOF on `ic`.

    val output_to_file_via_temporary : ?mode:open_flag list ->
           string -> (string -> out_channel -> 'a) -> 'a

Produce output in temporary file, then rename it (as atomically as possible) to the desired output file name. `output_to_file_via_temporary filename fn` opens a temporary file which is passed to `fn` (name + output channel). When `fn` returns, the channel is closed and the temporary file is renamed to `filename`.

    val protect_writing_to_file : filename:string -> f:(out_channel -> 'a) -> 'a

Open the given `filename` for writing (in binary mode), pass the `out_channel` to the given function, then close the channel. If the function raises an exception then `filename` will be removed.

    val concat_null_terminated : string list -> string

`concat_null_terminated [x1;x2; ... xn]` is `x1 ^ "\000" ^ x2 ^ "\000" ^ ... ^ xn ^ "\000"`

    val split_null_terminated : string -> string list

`split_null_terminated s` is similar `String.split_on_char '\000'` but ignores the trailing separator, if any

    val chop_extensions : string -> string

Return the given file name without its extensions. The extensions is the longest suffix starting with a period and not including a directory separator, `.xyz.uvw` for instance.

Return the given name if it does not contain an extension.

## Integer operations

    val log2 : int -> int

`log2 n` returns `s` such that `n = 1 lsl s` if `n` is a power of 2

    val align : int -> int -> int

`align n a` rounds `n` upwards to a multiple of `a` (a power of 2).

    val no_overflow_add : int -> int -> bool

`no_overflow_add n1 n2` returns `true` if the computation of `n1 + n2` does not overflow.

    val no_overflow_sub : int -> int -> bool

`no_overflow_sub n1 n2` returns `true` if the computation of `n1 - n2` does not overflow.

    val no_overflow_mul : int -> int -> bool

`no_overflow_mul n1 n2` returns `true` if the computation of `n1 * n2` does not overflow.

    val no_overflow_lsl : int -> int -> bool

`no_overflow_lsl n k` returns `true` if the computation of `n lsl k` does not overflow.

    val letter_of_int : int -> string

    module Int_literal_converter: sig .. end

    val find_first_mono : (int -> bool) -> int

`find_first_mono p` takes an integer predicate `p : int -> bool` that we assume: 1. is monotonic on natural numbers: if `a <= b` then `p a` implies `p b`, 2. is satisfied for some natural numbers in range `0; max_int` (this is equivalent to: `p max_int = true`).

`find_first_mono p` is the smallest natural number N that satisfies `p`, computed in O(log(N)) calls to `p`.

Our implementation supports two cases where the preconditions on `p` are not respected:

- If `p` is always `false`, we silently return `max_int` instead of looping or crashing.
- If `p` is non-monotonic but eventually true, we return some satisfying value.

## String operations

    val search_substring : string -> string -> int -> int

`search_substring pat str start` returns the position of the first occurrence of string `pat` in string `str`. Search starts at offset `start` in `str`. Raise `Not_found` if `pat` does not occur.

    val replace_substring : before:string -> after:string -> string -> string

`replace_substring ~before ~after str` replaces all occurrences of `before` with `after` in `str` and returns the resulting string.

    val rev_split_words : string -> string list

`rev_split_words s` splits `s` in blank-separated words, and returns the list of words in reverse order.

    val cut_at : string -> char -> string * string

`String.cut_at s c` returns a pair containing the sub-string before the first occurrence of `c` in `s`, and the sub-string after the first occurrence of `c` in `s`. `let (before, after) = String.cut_at s c in
before ^ String.make 1 c ^ after` is the identity if `s` contains `c`.

Raise `Not_found` if the character does not appear in the string

- Since 4.01

    val ordinal_suffix : int -> string

`ordinal_suffix n` is the appropriate suffix to append to the numeral `n` as an ordinal number: `1` -> `"st"`, `2` -> `"nd"`, `3` -> `"rd"`, `4` -> `"th"`, and so on. Handles larger numbers (e.g., `42` -> `"nd"`) and the numbers 11--13 (which all get `"th"`) correctly.

    val normalise_eol : string -> string

`normalise_eol s` returns a fresh copy of `s` with any '\r' characters removed. Intended for pre-processing text which will subsequently be printed on a channel which performs EOL transformations (i.e. Windows)

    val delete_eol_spaces : string -> string

`delete_eol_spaces s` returns a fresh copy of `s` with any end of line spaces removed. Intended to normalize the output of the toplevel for tests.

## Operations on references

    type ref_and_value =

`|` | `R : `'a ref * 'a` -> `ref_and_value``

    val protect_refs : ref_and_value list -> (unit -> 'a) -> 'a

`protect_refs l f` temporarily sets `r` to `v` for each `R (r, v)` in `l` while executing `f`. The previous contents of the references is restored even if `f` raises an exception, without altering the exception backtrace.

    val get_ref : 'a list ref -> 'a list

`get_ref lr` returns the content of the list reference `lr` and reset its content to the empty list.

    val set_or_ignore : ('a -> 'b option) -> 'b option ref -> 'a -> unit

`set_or_ignore f opt x` sets `opt` to `f x` if it returns `Some _`, or leaves it unmodified if it returns `None`.

## Operations on triples and quadruples

    val fst3 : 'a * 'b * 'c -> 'a

    val snd3 : 'a * 'b * 'c -> 'b

    val thd3 : 'a * 'b * 'c -> 'c

    val fst4 : 'a * 'b * 'c * 'd -> 'a

    val snd4 : 'a * 'b * 'c * 'd -> 'b

    val thd4 : 'a * 'b * 'c * 'd -> 'c

    val for4 : 'a * 'b * 'c * 'd -> 'd

## Spell checking and ``did you mean'' suggestions

    val edit_distance : string -> string -> int -> int option

`edit_distance a b cutoff` computes the edit distance between strings `a` and `b`. To help efficiency, it uses a cutoff: if the distance `d` is smaller than `cutoff`, it returns `Some d`, else `None`.

The distance algorithm currently used is Damerau-Levenshtein: it computes the number of insertion, deletion, substitution of letters, or swapping of adjacent letters to go from one word to the other. The particular algorithm may change in the future.

    val spellcheck : string list -> string -> string list

`spellcheck env name` takes a list of names `env` that exist in the current environment and an erroneous `name`, and returns a list of suggestions taken from `env`, that are close enough to `name` that it may be a typo for one of them.

    val align_hint : prefix:string ->
           main:Format_doc.t -> hint:Format_doc.t -> Format_doc.t * Format_doc.t

`aligned_hint main hint` vertically aligns a `main` message and a hint message. The vertical alignment is controlled by the use of `@{<ralign> ...
@}` boxes: the start of one box, in either the hint or the main message, will be shifted on the left to ensure that the end of the two boxes are vertically aligned, taking in account a pre-existing `prefix` before the main message. For instance,

    let main, sub =
      align_hint
        ~prefix:"Error: "
        (doc_printf "@{<ralign>The value @}%a is not an instance variable"
          Style.inline_code "foobar"
        )
        (doc_printf
          "@{<ralign>Did you mean @}%a" Style.inline_code "foobaz"
        ) in
       printf "Error: %a%a" pp_doc main pp_doc sub

produces the following text:

    Error:   The value "foobaz" is not an instance variable
    Hint: Did you mean "foobar"?

where the main message has been shifted to the left to align `"foobaz"` and `"foobar"`.

    val align_error_hint : main:Format_doc.t -> hint:Format_doc.t -> Format_doc.t * Format_doc.t

Same as `align_hint ~prefix:"Error: "`

    val aligned_hint : prefix:string ->
           Format_doc.formatter ->
           ('a, Format_doc.formatter, unit, Format_doc.t option -> unit) format4 ->
           'a

`aligned_hint ~prefix fmt ... hint` align the potential hint with the main error message generated by the format string `fmt` before printing the two message.

    val did_you_mean : ?pp:string Format_doc.printer -> string list -> Format_doc.t option

`did_you_mean ~pp choices` hints that the user may have meant one of the option in `choices`.

Each choice is printed with the `pp` function, or `Style.inline_code` if `pp`=`None`.

    module Color: sig .. end

Color support detection

## Styling handling for terminal output

    module Style: sig .. end

    module Error_style: sig .. end

## Formatted output

    val print_if : Format.formatter ->
           bool ref -> (Format.formatter -> 'a -> unit) -> 'a -> 'a

`print_if ppf flag fmt x` prints `x` with `fmt` on `ppf` if `b` is true.

    val print_see_manual : int list Format_doc.printer

See manual section

## Displaying configuration variables

    val show_config_and_exit : unit -> unit

Display the values of all compiler configuration variables from module `Config`, then exit the program with code 0.

    val show_config_variable_and_exit : string -> unit

Display the value of the given configuration variable, then exit the program with code 0.

## Handling of build maps

Build maps cause the compiler to normalize file names embedded in object files, thus leading to more reproducible builds.

    val get_build_path_prefix_map : unit -> Build_path_prefix_map.map option

Returns the map encoded in the `BUILD_PATH_PREFIX_MAP` environment variable.

    val invert_build_path_prefix_map : string -> string list

Returns the potential paths (in priority order) from which the given path can originate from before rewrite using `BUILD_PATH_PREFIX_MAP` environment variable.

    val debug_prefix_map_flags : unit -> string list

Returns the list of `--debug-prefix-map` flags to be passed to the assembler, built from the `BUILD_PATH_PREFIX_MAP` environment variable.

## Handling of magic numbers

    module Magic_number: sig .. end

## Minimal support for Unicode characters in identifiers

Characters allowed in identifiers are, currently:

- ASCII letters A-Z a-z
- Latin-1 letters (U+00C0 - U+00FF except U+00D7 and U+00F7)
- Character sequences which normalize to the above character under NFC
- digits 0-9, underscore, single quote

    module Utf8_lexeme: sig .. end

    module RuntimeID: sig .. end

## Miscellaneous type aliases

    type filepath = string

    type modname = string

    type crcs = (modname * Digest.BLAKE128.t option) list

    type alerts = string Stdlib.String.Map.t