72 lines
1.6 KiB
Plaintext
72 lines
1.6 KiB
Plaintext
pub hkt Monad[T<A>] {
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fn <B> map(m: fn (from: A) => B): T<B>
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fn <B> flat_map(m: fn (from: A) => T<B>): T<B>
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}
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pub hkt Monad[T<A, B>] : Monad[T<B>] {
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fn map_left(m: fn (left: A) => B): T<B>
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fn flat_map_left(m: fn (left: A) => T<B>): T<B>
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}
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pub enum Option<T> : Monad {
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Some(item: T) {
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impl fn map(m) = Some(m(item))
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impl fn flat_map(m) = m(item)
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},
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None {
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impl fn map(m) = self
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impl fn flat_map(m) = self
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}
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}
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pub enum Either<E, A> : Monad {
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Left(e: E) {
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impl fn map(m) = self
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impl fn flat_map(m) = self
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impl fn map_left(m) = Right(m(e))
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impl fn flat_map_left(m) = m(e)
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},
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Right(a: A) {
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impl fn map(m) = Right(m(a))
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impl fn flat_map(m) = m(a)
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impl fn map_left(m) = self
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impl fn flat_map_left(m) = self
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}
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}
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// Usage of Either in a file interface.
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pub int File {
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name: String
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fn read_data(): String
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fn close()
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}
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#target[lua]
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impl LuaFile(name: String, fld file: LuaObject) : File {
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impl fn read_data() = lua {% $file.readAll() %}
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impl fn close() = lua {% $file.close() %}
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}
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#target[lua]
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pub fn open_file(name: String): Either<Error, File> {
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try {
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Right(LuaFile(name, lua {% fs.open($name) %}))
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} catch (e: LuaError) {
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Left(e)
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}
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}
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// Usage in a main file, perhaps.
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// Note this part would be platform independent.
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let data_length = match open_file('test.txt') {
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Left(error) => println(error.message),
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Right(file) => {
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let data_length = f.read_data().length()
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f.close()
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data_length
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}
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}
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println(data_length)
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