Work on hkt and int.

sketching/hkt.dm

@@ -1,69 +1,40 @@
-// Use this one!
+pub hkt Monad[T<A>] {
-pub int Unit
+    fn <B> map(m: fn (from: A) => B): T<B>
-
+    fn <B> flat_map(m: fn (from: A) => T<B>): T<B>
-pub hkt Identity {
-    fn identity() = Self
 }
 
-pub int Addable<T : Addable<T>> {
+pub hkt Monad[T<A, B>] : Monad[T<B>] {
-    fn op+(other: T): T
+    fn map_left(m: fn (left: A) => B): T<B>
+    fn flat_map_left(m: fn (left: A) => T<B>): T<B>
 }
 
-pub hkt Monoid<A : Addable<A>>(a: A) : Identity {
+pub enum Option<T> : Monad {
-    fn concat(other: Self) = Self(a + other.a)
+    Some(item) {
-}
+        impl fn map(m) = Some(m(item))
-
+        impl fn flat_map(m) = m(item)
-pub hkt Monad1<A>(item: A) {
-    fn <B> map(m: fn (from: A): B) = item is A ? Self(m(item)) : self
-    fn <B> flat_map(m: fn (from: A): T<B>) = item is A ? m(item) : self
-}
-
-pub hkt Monad2<A, B>(item: A | B) : Monad1<A>(item is A ? item : Unit) {
-    fn map_right(m: fn (right: B): B) = item is B ? Self(m(item)) : self
-    fn flat_map_right(m: fn (right: B): Self) = item is B ? m(item) : self
-    fn fold_right(f: fn (right: B): A) = item is B ? Self(f(item)) : self
-}
-
-pub hkt Reader2<R, A, B>(readable: R, item: A, other: B) : Monad2<A, B>(item) {
-    fn read(reader: fn (readable: R): A) = Self(readable, reader(readable), other)
-    fn use(user: fn (readable: R): Unit) = Self(readable, user(readable), other)
-}
-
-pub enum type Option<T> : Monad1 {
-    Some(item),
-    None
-}
-
-pub enum type IO<T, E> : Monad2 {
-    Success(item: T),
-    Failure(error: E)
-}
-
-// usage in a file interface
-pub fn open_file(name: String): FileReader<Unit> {
-    try {
-        let file: LuaObject = lua {% fs.open(${name}) %}
-        return Success(
-            File {
-                name,
-                impl fn read_data() {
-                    lua {% ${file}.readAll() %}
-                }
-                impl fn close() {
-                    lua {% ${file}.close() %}
-                }
     },
-            Unit
+    None {
-        )
+        impl fn map(m) = self
-    } catch (e: LuaError) {
+        impl fn flat_map(m) = self
-        return Failure(e)
     }
 }
 
-pub enum type FileReader<R, E> : Reader2<File, R, E> {
+pub enum Either<E, A> : Monad {
-    Success(file: File, result: R) : Super(file, result, Unit),
+    Left(e: E) {
-    Failure(error: E) : Super(file, Unit, error)
+        impl fn map(m) = self
+        impl fn flat_map(m) = self
+        impl fn map_left(m) = Right(m(e))
+        impl fn flat_map_left(m) = m(e)
+    },
+    Right(a: A) {
+        impl fn map(m) = Right(m(a))
+        impl fn flat_map(m) = m(a)
+        impl fn map_left(m) = self
+        impl fn flat_map_left(m) = self
     }
+}
+
+// Usage of Either in a file interface.
 
 pub int File {
     name: String
@@ -71,18 +42,30 @@ pub int File {
     fn close()
 }
 
-// usage in a main file, perhaps
+#target[lua]
+impl LuaFile(name: String, fld file: LuaObject) : File {
+    impl fn read_data() = lua {% ${file}.readAll() %}
+    impl fn close() = lua {% ${file}.close() %}
+}
 
-match open_file('test.txt')
+#target[lua]
-    .read { f -> f.read_data() }
+pub fn open_file(name: String): Either<Error, File> {
-    .map { data -> data.length() }
+    try {
-{
+        Right(LuaFile(name, lua {% fs.open($name) %}))
-    Success(file, length) => {
+    } catch (e: LuaError) {
+        Left(e)
+    }
+}
+
+// Usage in a main file, perhaps.
+// Note this part would be platform independent.
+
+let data_length = match open_file('test.txt') {
+    Left(error) => println(error.message),
+    Right(file) => {
+        let data_length = f.read_data().length()
         f.close()
-        println(result)
+        data_length
-    },
-    Failure(error) => {
-        println(error.message)
     }
 }
-
+println(data_length)

sketching/int.dm

@@ -0,0 +1,33 @@
+/* Some basic interfaces, representing some useful functional concepts. */
+
+/**
+ * Represents a "zero" for addition, for example, or a "one" for multiplication, for example
+ */
+pub int Identity<A> {
+    identity: A // a constant prop. By default, all props are immutable.
+}
+
+/**
+ * This shows how to do operator overloading via an interface
+ */
+pub int Addable<T : Addable<T>> {
+    fn op+(other: T): T // a function which must be implemented by inheritors
+}
+
+/**
+ * Represents a struct that can do concatenation of values.
+ */
+pub int Monoid<A> : Identity {
+    fn concat(first: A, second: A): A
+}
+
+decl pub int Number : Addable<Number> // primitive
+
+// example usage
+decl fn <T> assert_eq(expected: T, actual: T)
+
+let add_monoid: Monoid<Number> = Monoid {
+    identity: 0
+    impl fn concat(a, b) = a + b
+}
+assert_eq(2, add_monoid.concat(1, 1))