Error matching literal single bits

[devesascampos]

(Apols in advance if I'm doing something really dumb)

Have (ppx_)bitstring version 4.1.0 on ocaml 4.11.2

<><> bitstring: information on all versions <><><><><><><><><><><><><><><><>  🐫 
name                   bitstring
all-installed-versions 4.1.0 [default]

Trying to match a bitstring bs with a pattern containing/consisting of a single literal bit fails:

# let bs = Bitstring.bitstring_of_string "a";;
val bs : Bitstring.bitstring = (Bytes.of_string "a", 0, 8)
# match%bitstring bs with | {| 0:1 |} -> "working";;
Error: This pattern matches values of type int
       but a pattern was expected which matches values of type bool

(the {| appears underlined)

In fact, something like the pattern_matcher example in documentation.md also fails

# let pattern_matcher = function%bitstring
  | {| 1 : 1
     ; a : 2
     ; b : 16 : bigendian
  |} -> true
  | {| _ |} -> false
  ;;
Error: This pattern matches values of type int
       but a pattern was expected which matches values of type bool

(the {| appears underlined)

Replacing the literal with a variable works

# match%bitstring bs with | {| x:1 |} -> "working";;
- : string = "working"

And then adding a check serves as a workaround to get the original intent

# match%bitstring bs with | {| x:1:check(x = false) |} -> "working";;
- : string = "working"

but is clunky.

[devesascampos]

I understand if this is expected behaviour (and the example is wrong) and I should just use bools

# match%bitstring bs with | {| false:1: |} -> "working";;
- : string = "working"
# match%bitstring bs with | {| true:1: |} -> "working";;
Exception: Match_failure ("//toplevel//", 1, 0).

but to me it strikes me as weird to be able to match 0b01 but not 0b0 particularly when matching longer patterns that contain longer sections of literal bits.

[xguerin]

~Looks like an oversight, thanks for reporting. I'll look into it.~ The documentation is inaccurate. Since the migration to PPX, single-bit values are interpreted as bool. The following does work:

let match_bits_with_expected_values _ =
    (*
     * Create a string of bits.
     *)
    let bits = Bitstring.bitstring_of_string "a" in 
    (*
     * Match expected bits.
     *)
    let actual = match%bitstring bits with
     | {| false:1 ; true:1 ; _ : -1 : bitstring |} -> true
     | {| _ |} -> false
    in
    assert actual

[devesascampos]

Thx for the clarification.