std/stream: add Extent() and tweak Drain() (#173)

* std/stream: make `Drain()` return the last value instead of the stream

Closes #172.

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

* wdte: Update some dependencies.

go.mod

@@ -3,5 +3,5 @@ module github.com/DeedleFake/wdte
 require (
 	github.com/peterh/liner v1.1.0
 	golang.org/x/crypto v0.0.0-20181203042331-505ab145d0a9
-	golang.org/x/sys v0.0.0-20181205085412-a5c9d58dba9a // indirect
+	golang.org/x/sys v0.0.0-20181206074257-70b957f3b65e // indirect
 )

go.sum

@@ -4,5 +4,5 @@ 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 v0.0.0-20181203042331-505ab145d0a9 h1:mKdxBk7AujPs8kU4m80U72y/zjbZ3UcXC7dClwKbUI0=
 golang.org/x/crypto v0.0.0-20181203042331-505ab145d0a9/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
-golang.org/x/sys v0.0.0-20181205085412-a5c9d58dba9a h1:1n5lsVfiQW3yfsRGu98756EH1YthsFqr/5mxHduZW2A=
-golang.org/x/sys v0.0.0-20181205085412-a5c9d58dba9a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20181206074257-70b957f3b65e h1:njOxP/wVblhCLIUhjHXf6X+dzTt5OQ3vMQo9mkOIKIo=
+golang.org/x/sys v0.0.0-20181206074257-70b957f3b65e/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=

std/stream/end.go

@@ -1,6 +1,8 @@
 package stream
 
 import (
+	"sort"
+
 	"github.com/DeedleFake/wdte"
 	"github.com/DeedleFake/wdte/auto"
 )
@@ -79,14 +81,18 @@ func Drain(frame wdte.Frame, args ...wdte.Func) wdte.Func {
 	}
 
 	s := args[0].Call(frame).(Stream)
+
+	last := End()
 	for {
 		n, ok := s.Next(frame)
 		if !ok {
-			return s
+			return last
 		}
 		if _, ok := n.(error); ok {
 			return n
 		}
+
+		last = n
 	}
 }
 
@@ -158,6 +164,70 @@ func Fold(frame wdte.Frame, args ...wdte.Func) wdte.Func {
 	return Reduce(frame, s, cur, r)
 }
 
+// Extent is a WDTE function with the following signatures:
+//
+//    extent s n less
+//    (extent n less) s
+//    (extent less) s n
+//    ((extent less) n) s
+//
+// It drains the Stream s, building up a list of up to n elements
+// yielded for which less returns true compared to other elements in
+// the list, sorted such that the first element of the list is the
+// most less of them. In other words, it returns the n most minimum
+// elements using less to perform the compartison. For example,
+//
+//    range 10 -> extent 3 >
+//
+// will return [9; 8; 7].
+func Extent(frame wdte.Frame, args ...wdte.Func) wdte.Func {
+	frame = frame.Sub("extent")
+
+	if len(args) < 3 {
+		return auto.SaveArgsReverse(wdte.GoFunc(Extent), args...)
+	}
+
+	s := args[0].Call(frame).(Stream)
+	length := args[1].Call(frame).(wdte.Number)
+	less := args[2].Call(frame)
+
+	var c func(wdte.Array, int, wdte.Func) wdte.Array
+	c = func(extent wdte.Array, i int, f wdte.Func) wdte.Array {
+		extent = append(extent[:i], append(wdte.Array{f}, extent[i:len(extent)-1]...)...)
+
+		if len(extent) == int(length) {
+			c = func(extent wdte.Array, i int, f wdte.Func) wdte.Array {
+				copy(extent[i:], extent[i+1:])
+				extent[i] = f
+				return extent
+			}
+		}
+
+		return extent
+	}
+
+	extent := make(wdte.Array, 0, int(length))
+	for {
+		n, ok := s.Next(frame)
+		if !ok {
+			return extent
+		}
+		n = n.Call(frame)
+
+		i := sort.Search(len(extent), func(i int) bool {
+			return less.Call(frame, n, extent[i]) == wdte.Bool(true)
+		})
+		if i < len(extent) {
+			extent = c(extent, i, n)
+			continue
+		}
+
+		if len(extent) < int(length) {
+			extent = append(extent, n)
+		}
+	}
+}
+
 // TODO: Implement this. It should be able to essentially insert its
 // own output into another chain, so that
 //

std/stream/stream.go

@@ -55,6 +55,7 @@ var Scope = wdte.S().Map(map[wdte.ID]wdte.Func{
 	"drain":   wdte.GoFunc(Drain),
 	"reduce":  wdte.GoFunc(Reduce),
 	"fold":    wdte.GoFunc(Fold),
+	"extent":  wdte.GoFunc(Extent),
 	//"chain":   wdte.GoFunc(Chain),
 	"any": wdte.GoFunc(Any),
 	"all": wdte.GoFunc(All),

wdte_test.go

@@ -534,9 +534,18 @@ func TestStream(t *testing.T) {
 			},
 		},
 		{
-			name:   "Drain",
-			script: `let s => import 'stream'; let io => import 'io'; let main => s.range 5 -> s.map (io.writeln io.stdout) -> s.drain;`,
-			out:    "0\n1\n2\n3\n4\n",
+			name: "Drain",
+			script: `
+				let s => import 'stream';
+				let io => import 'io';
+				let main =>
+					s.range 5
+					-> s.map (@ p v => io.writeln io.stdout v; v)
+					-> s.drain
+					;
+				`,
+			ret: wdte.Number(4),
+			out: "0\n1\n2\n3\n4\n",
 		},
 		{
 			name:   "Reduce",
@@ -548,6 +557,16 @@ func TestStream(t *testing.T) {
 			script: `let s => import 'stream'; s.range 5 -> s.fold +;`,
 			ret:    wdte.Number(10),
 		},
+		{
+			name:   "Extent/Min",
+			script: `let s => import 'stream'; let a => import 'arrays'; a.stream [5; 3; 6; 2; 7; 1] -> s.extent 3 <;`,
+			ret:    wdte.Array{wdte.Number(1), wdte.Number(2), wdte.Number(3)},
+		},
+		{
+			name:   "Extent/Max",
+			script: `let s => import 'stream'; let a => import 'arrays'; a.stream [5; 3; 6; 2; 7; 1] -> s.extent 3 >;`,
+			ret:    wdte.Array{wdte.Number(7), wdte.Number(6), wdte.Number(5)},
+		},
 		{
 			name:   "Any/True",
 			script: `let s => import 'stream'; let main => s.range 5 -> s.any (== 3);`,