refactor: introduce Source trait for random generator

Author: peter-jerry-ye

random/README.mbt.md

@@ -7,7 +7,7 @@ Internally, it uses the `Chacha8` cipher to generate random numbers. It is a cry
 # Usage
 
 ```moonbit
-  let r = @random.new()
+  let r = @random.Rand::new(@random.chacha8())
   assert_eq!(r.uint(limit=10), 7)
   assert_eq!(r.uint(limit=10), 0)
   assert_eq!(r.uint(limit=10), 5)

random/random.mbt

@@ -13,36 +13,57 @@
 // limitations under the License.
 
 ///|
-/// Currently we only support [chacha8] as the source of randomness.
-struct Rand {
-  src : @random_source.ChaCha8
+/// `Rand` is a pseudo-random number generator (PRNG) that provides various
+/// methods to generate random numbers of different types.
+type Rand &Source
+
+///|
+/// The [Source] trait defines a method to generate random numbers.
+pub(open) trait Source {
+  next(Self) -> UInt64
+}
+
+///|
+impl Source for @random_source.ChaCha8 with next(self : @random_source.ChaCha8) -> UInt64 {
+  for {
+    let x = self.state.next()
+    if x.1 {
+      return x.0
+    }
+    self.state.refill()
+  }
 }
 
 ///|
 /// Create a new random number generator with [seed].
 /// @alert unsafe "Panic if seed is not 32 bytes long"
+#deprecated("Use `Rand::new(chacha8())` instead")
 pub fn new(seed~ : Bytes = b"ABCDEFGHIJKLMNOPQRSTUVWXYZ123456") -> Rand {
   if seed.length() != 32 {
     abort("seed must be 32 bytes long")
   }
-  let src = @random_source.ChaCha8::new(seed)
-  { src, }
+  @random_source.ChaCha8::new(seed) as &Source
+}
+
+///|
+/// Create a new random number generator with [seed].
+/// @alert unsafe "Panic if seed is not 32 bytes long"
+pub fn chacha8(seed~ : Bytes = b"ABCDEFGHIJKLMNOPQRSTUVWXYZ123456") -> &Source {
+  if seed.length() != 32 {
+    abort("seed must be 32 bytes long")
+  }
+  @random_source.ChaCha8::new(seed) as &Source
 }
 
-///| @alert deprecated "use `@random.new` instead"
-pub fn Rand::new(seed~ : Bytes = b"ABCDEFGHIJKLMNOPQRSTUVWXYZ123456") -> Rand {
-  new(seed~)
+///|
+/// Create a new random number generator with a given [Gen] source.
+pub fn Rand::new(generator : &Source) -> Rand {
+  generator
 }
 
 ///|
 fn next(self : Rand) -> UInt64 {
-  for {
-    let x = self.src.state.next()
-    if x.1 {
-      return x.0
-    }
-    self.src.state.refill()
-  }
+  self._.next()
 }
 
 ///|

random/random.mbti

@@ -1,6 +1,8 @@
 package "moonbitlang/core/random"
 
 // Values
+fn chacha8(seed~ : Bytes = ..) -> &Source
+
 fn double(Rand) -> Double
 
 fn float(Rand) -> Float
@@ -9,6 +11,7 @@ fn int(Rand, limit~ : Int = ..) -> Int
 
 fn int64(Rand, limit~ : Int64 = ..) -> Int64
 
+#deprecated
 fn new(seed~ : Bytes = ..) -> Rand
 
 fn shuffle(Rand, Int, (Int, Int) -> Unit) -> Unit
@@ -24,7 +27,7 @@ impl Rand {
   float(Self) -> Float
   int(Self, limit~ : Int = ..) -> Int
   int64(Self, limit~ : Int64 = ..) -> Int64
-  new(seed~ : Bytes = ..) -> Self //deprecated
+  new(&Source) -> Self
   shuffle(Self, Int, (Int, Int) -> Unit) -> Unit
   uint(Self, limit~ : UInt = ..) -> UInt
   uint64(Self, limit~ : UInt64 = ..) -> UInt64
@@ -33,4 +36,7 @@ impl Rand {
 // Type aliases
 
 // Traits
+pub(open) trait Source {
+  next(Self) -> UInt64
+}