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bit_builder.gleam
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bit_builder.gleam
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//// BitBuilder is a type used for efficiently concatenating bits to create bit
//// strings.
////
//// If we append one bit string to another the bit strings must be copied to a
//// new location in memory so that they can sit together. This behaviour
//// enables efficient reading of the string but copying can be expensive,
//// especially if we want to join many bit strings together.
////
//// BitBuilder is different in that it can be joined together in constant
//// time using minimal memory, and then can be efficiently converted to a
//// bit string using the `to_bit_string` function.
////
//// On Erlang this type is compatible with Erlang's iolists.
import gleam/string_builder.{StringBuilder}
if javascript {
import gleam/list
import gleam/bit_string
}
if erlang {
pub external type BitBuilder
}
if javascript {
pub opaque type BitBuilder {
Bits(BitString)
Text(StringBuilder)
Many(List(BitBuilder))
}
}
/// Create an empty `BitBuilder`. Useful as the start of a pipe chaning many
/// builders together.
///
pub fn new() -> BitBuilder {
do_concat([])
}
/// Prepends a bit string to the start of a builder.
///
/// Runs in constant time.
///
pub fn prepend(to: BitBuilder, prefix: BitString) -> BitBuilder {
append_builder(from_bit_string(prefix), to)
}
/// Appends a bit string to the end of a builder.
///
/// Runs in constant time.
///
pub fn append(to: BitBuilder, suffix: BitString) -> BitBuilder {
append_builder(to, from_bit_string(suffix))
}
/// Prepends a builder onto the start of another.
///
/// Runs in constant time.
///
pub fn prepend_builder(to: BitBuilder, prefix: BitBuilder) -> BitBuilder {
append_builder(prefix, to)
}
/// Appends a builder onto the end of another.
///
/// Runs in constant time.
///
pub fn append_builder(
to first: BitBuilder,
suffix second: BitBuilder,
) -> BitBuilder {
do_append_builder(first, second)
}
if erlang {
external fn do_append_builder(
to: BitBuilder,
suffix: BitBuilder,
) -> BitBuilder =
"gleam_stdlib" "iodata_append"
}
if javascript {
fn do_append_builder(first: BitBuilder, second: BitBuilder) -> BitBuilder {
case second {
Many(builders) -> Many([first, ..builders])
_ -> Many([first, second])
}
}
}
/// Prepends a string onto the start of a builder.
///
/// Runs in constant time when running on Erlang.
/// Runs in linear time with the length of the string otherwise.
///
pub fn prepend_string(to: BitBuilder, prefix: String) -> BitBuilder {
append_builder(from_string(prefix), to)
}
/// Appends a string onto the end of a builder.
///
/// Runs in constant time when running on Erlang.
/// Runs in linear time with the length of the string otherwise.
///
pub fn append_string(to: BitBuilder, suffix: String) -> BitBuilder {
append_builder(to, from_string(suffix))
}
/// Joins a list of builders into a single builder.
///
/// Runs in constant time.
///
pub fn concat(builders: List(BitBuilder)) -> BitBuilder {
do_concat(builders)
}
if erlang {
external fn do_concat(List(BitBuilder)) -> BitBuilder =
"gleam_stdlib" "identity"
}
if javascript {
fn do_concat(builders: List(BitBuilder)) -> BitBuilder {
Many(builders)
}
}
/// Joins a list of bit strings into a single builder.
///
/// Runs in constant time.
///
pub fn concat_bit_strings(bits: List(BitString)) -> BitBuilder {
do_concat_bit_strings(bits)
}
if erlang {
external fn do_concat_bit_strings(List(BitString)) -> BitBuilder =
"gleam_stdlib" "identity"
}
if javascript {
fn do_concat_bit_strings(bits: List(BitString)) -> BitBuilder {
bits
|> list.map(fn(b) { from_bit_string(b) })
|> concat()
}
}
/// Creates a new builder from a string.
///
/// Runs in constant time when running on Erlang.
/// Runs in linear time otherwise.
///
pub fn from_string(string: String) -> BitBuilder {
do_from_string(string)
}
if erlang {
external fn do_from_string(String) -> BitBuilder =
"gleam_stdlib" "wrap_list"
}
if javascript {
fn do_from_string(string: String) -> BitBuilder {
Text(string_builder.from_string(string))
}
}
/// Creates a new builder from a string builder.
///
/// Runs in constant time when running on Erlang.
/// Runs in linear time otherwise.
///
pub fn from_string_builder(builder: StringBuilder) -> BitBuilder {
do_from_string_builder(builder)
}
if erlang {
external fn do_from_string_builder(StringBuilder) -> BitBuilder =
"gleam_stdlib" "wrap_list"
}
if javascript {
fn do_from_string_builder(builder: StringBuilder) -> BitBuilder {
Text(builder)
}
}
/// Creates a new builder from a bit string.
///
/// Runs in constant time.
///
pub fn from_bit_string(bits: BitString) -> BitBuilder {
do_from_bit_string(bits)
}
if erlang {
external fn do_from_bit_string(BitString) -> BitBuilder =
"gleam_stdlib" "wrap_list"
}
if javascript {
fn do_from_bit_string(bits: BitString) -> BitBuilder {
Bits(bits)
}
}
/// Turns an builder into a bit string.
///
/// Runs in linear time.
///
/// When running on Erlang this function is implemented natively by the
/// virtual machine and is highly optimised.
///
pub fn to_bit_string(builder: BitBuilder) -> BitString {
do_to_bit_string(builder)
}
if erlang {
external fn do_to_bit_string(BitBuilder) -> BitString =
"erlang" "list_to_bitstring"
}
if javascript {
fn do_to_bit_string(builder: BitBuilder) -> BitString {
[[builder]]
|> to_list([])
|> list.reverse
|> bit_string.concat
}
fn to_list(
stack: List(List(BitBuilder)),
acc: List(BitString),
) -> List(BitString) {
case stack {
[] -> acc
[[], ..remaining_stack] -> to_list(remaining_stack, acc)
[[Bits(bits), ..rest], ..remaining_stack] ->
to_list([rest, ..remaining_stack], [bits, ..acc])
[[Text(builder), ..rest], ..remaining_stack] -> {
let bits = bit_string.from_string(string_builder.to_string(builder))
to_list([rest, ..remaining_stack], [bits, ..acc])
}
[[Many(builders), ..rest], ..remaining_stack] ->
to_list([builders, rest, ..remaining_stack], acc)
}
}
}
/// Returns the size of the builder's content in bytes.
///
/// Runs in linear time.
///
pub fn byte_size(builder: BitBuilder) -> Int {
do_byte_size(builder)
}
if erlang {
external fn do_byte_size(BitBuilder) -> Int =
"erlang" "iolist_size"
}
if javascript {
fn do_byte_size(builder: BitBuilder) -> Int {
[[builder]]
|> to_list([])
|> list.fold(0, fn(acc, builder) { bit_string.byte_size(builder) + acc })
}
}