std/stream: fold, repeat, and limit (#165)

* std/stream: Add `Fold()`.

* std/stream: Add `Repeat()` and `Limit()`.

* wdte: Update some dependencies.

go.mod

@@ -2,6 +2,6 @@ module github.com/DeedleFake/wdte
 
 require (
 	github.com/peterh/liner v1.1.0
-	golang.org/x/crypto v0.0.0-20181112202954-3d3f9f413869
-	golang.org/x/sys v0.0.0-20181107165924-66b7b1311ac8 // indirect
+	golang.org/x/crypto v0.0.0-20181127143415-eb0de9b17e85
+	golang.org/x/sys v0.0.0-20181128092732-4ed8d59d0b35 // indirect
 )

go.sum

@@ -2,7 +2,7 @@ github.com/mattn/go-runewidth v0.0.3 h1:a+kO+98RDGEfo6asOGMmpodZq4FNtnGP54yps8Bz
 github.com/mattn/go-runewidth v0.0.3/go.mod h1:LwmH8dsx7+W8Uxz3IHJYH5QSwggIsqBzpuz5H//U1FU=
 github.com/peterh/liner v1.1.0 h1:f+aAedNJA6uk7+6rXsYBnhdo4Xux7ESLe+kcuVUF5os=
 github.com/peterh/liner v1.1.0/go.mod h1:CRroGNssyjTd/qIG2FyxByd2S8JEAZXBl4qUrZf8GS0=
-golang.org/x/crypto v0.0.0-20181112202954-3d3f9f413869 h1:kkXA53yGe04D0adEYJwEVQjeBppL01Exg+fnMjfUraU=
-golang.org/x/crypto v0.0.0-20181112202954-3d3f9f413869/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
-golang.org/x/sys v0.0.0-20181107165924-66b7b1311ac8 h1:YoY1wS6JYVRpIfFngRf2HHo9R9dAne3xbkGOQ5rJXjU=
-golang.org/x/sys v0.0.0-20181107165924-66b7b1311ac8/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/crypto v0.0.0-20181127143415-eb0de9b17e85 h1:et7+NAX3lLIk5qUCTA9QelBjGE/NkhzYw/mhnr0s7nI=
+golang.org/x/crypto v0.0.0-20181127143415-eb0de9b17e85/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
+golang.org/x/sys v0.0.0-20181128092732-4ed8d59d0b35 h1:YAFjXN64LMvktoUZH9zgY4lGc/msGN7HQfoSuKCgaDU=
+golang.org/x/sys v0.0.0-20181128092732-4ed8d59d0b35/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=

std/stream/end.go

@@ -132,6 +132,32 @@ func Reduce(frame wdte.Frame, args ...wdte.Func) wdte.Func {
 	}
 }
 
+// Fold is a WDTE function with the following signatures:
+//
+//    fold s r
+//    (fold r) s
+//
+// Fold is exactly like Reduce, but is uses the first element of the
+// Stream s as its initial element, rather than taking an explicit
+// one. If there is no first element, it returns End.
+func Fold(frame wdte.Frame, args ...wdte.Func) wdte.Func {
+	frame = frame.Sub("fold")
+
+	if len(args) < 2 {
+		return auto.SaveArgsReverse(wdte.GoFunc(Fold), args...)
+	}
+
+	s := args[0].Call(frame).(Stream)
+	cur, ok := s.Next(frame)
+	if !ok {
+		return End()
+	}
+
+	r := args[1]
+
+	return Reduce(frame, s, cur, r)
+}
+
 // TODO: Implement this. It should be able to essentially insert its
 // own output into another chain, so that
 //

std/stream/middle.go

@@ -161,3 +161,88 @@ func Enumerate(frame wdte.Frame, args ...wdte.Func) wdte.Func {
 		return r, true
 	})
 }
+
+// Repeat is a WDTE function with the following signature:
+//
+//    repeat s
+//
+// Repeat returns a Stream that buffers the elements from the Stream
+// s. Once s has ended, the Stream starts repeating from the begnning
+// of the buffer, looping infinitely. In other words,
+//
+//    range 3 -> repeat
+//
+// will yield the sequence (0, 1, 2) repeatedly with no end.
+//
+// Repeat is most useful used with Limit. When combining the two, note
+// that Limit limits individual elements, not repetitions, so the
+// number passed to Limit should be multiplied properly if the client
+// wants to limit to a specific number of repetitions.
+func Repeat(frame wdte.Frame, args ...wdte.Func) wdte.Func {
+	frame = frame.Sub("repeat")
+
+	switch len(args) {
+	case 0:
+		return wdte.GoFunc(Repeat)
+	}
+
+	s := args[0].Call(frame).(Stream)
+
+	var buf []wdte.Func
+	loop := -1
+	return NextFunc(func(frame wdte.Frame) (wdte.Func, bool) {
+		frame = frame.Sub("repeat")
+
+	exit:
+		if loop >= 0 {
+			n := buf[loop]
+
+			loop++
+			loop %= len(buf)
+
+			return n, true
+		}
+
+		n, ok := s.Next(frame)
+		if !ok {
+			loop = 0
+			goto exit
+		}
+
+		buf = append(buf, n)
+		return n, true
+	})
+}
+
+// Limit is a WDTE function with the following signature:
+//
+//    (limit n) s
+//
+// Limit returns a Stream that stops after a maximum of n elements
+// from s have been yielded.
+func Limit(frame wdte.Frame, args ...wdte.Func) wdte.Func {
+	frame = frame.Sub("limit")
+
+	if len(args) == 0 {
+		return wdte.GoFunc(Limit)
+	}
+
+	n := args[0].Call(frame).(wdte.Number)
+
+	return wdte.GoFunc(func(frame wdte.Frame, args ...wdte.Func) wdte.Func {
+		frame = frame.Sub("limit")
+
+		s := args[0].Call(frame).(Stream)
+
+		return NextFunc(func(frame wdte.Frame) (wdte.Func, bool) {
+			frame = frame.Sub("limit")
+
+			if n <= 0 {
+				return nil, false
+			}
+			n--
+
+			return s.Next(frame)
+		})
+	})
+}

std/stream/stream.go

@@ -47,11 +47,14 @@ var Scope = wdte.S().Map(map[wdte.ID]wdte.Func{
 	"filter":    wdte.GoFunc(Filter),
 	"flatMap":   wdte.GoFunc(FlatMap),
 	"enumerate": wdte.GoFunc(Enumerate),
+	"repeat":    wdte.GoFunc(Repeat),
+	"limit":     wdte.GoFunc(Limit),
 
 	"end":     End(),
 	"collect": wdte.GoFunc(Collect),
 	"drain":   wdte.GoFunc(Drain),
 	"reduce":  wdte.GoFunc(Reduce),
+	"fold":    wdte.GoFunc(Fold),
 	//"chain":   wdte.GoFunc(Chain),
 	"any": wdte.GoFunc(Any),
 	"all": wdte.GoFunc(All),

wdte_test.go

@@ -519,6 +519,15 @@ func TestStream(t *testing.T) {
 				wdte.Array{wdte.Number(2), wdte.String("c")},
 			},
 		},
+		{
+			name:   "RepeatAndLimit",
+			script: `let s => import 'stream'; s.range 3 -> s.repeat -> s.limit 9 -> s.collect;`,
+			ret: wdte.Array{
+				wdte.Number(0), wdte.Number(1), wdte.Number(2),
+				wdte.Number(0), wdte.Number(1), wdte.Number(2),
+				wdte.Number(0), wdte.Number(1), wdte.Number(2),
+			},
+		},
 		{
 			name:   "Drain",
 			script: `let s => import 'stream'; let io => import 'io'; let main => s.range 5 -> s.map (io.writeln io.stdout) -> s.drain;`,
@@ -529,6 +538,11 @@ func TestStream(t *testing.T) {
 			script: `let s => import 'stream'; let main => s.range 1 6 -> s.reduce 1 *;`,
 			ret:    wdte.Number(120),
 		},
+		{
+			name:   "Fold",
+			script: `let s => import 'stream'; s.range 5 -> s.fold +;`,
+			ret:    wdte.Number(10),
+		},
 		{
 			name:   "Any/True",
 			script: `let s => import 'stream'; let main => s.range 5 -> s.any (== 3);`,