JS streams

JS streams.js

function intStream(from, to) {
    var i = from;
    var unbounded = ("number" !== typeof to);
    return {
        hasNext: function() { return unbounded ? true : (i < to); },
        next: function() { if (!this.hasNext()) throw "Stream Finished"; return i++; },
        toString: function() {
            return "Int Stream: from " + from + ", " + (unbounded ? "unbounded" : "to " + to);
        }
    };
}

function mapStream(stream, mapper, mapperDesc) {
    return {
        hasNext: function() { return stream.hasNext(); },
        next: function() { return mapper(stream.next()); },
        toString: function() {
            return "Mapped Stream: from <" + stream + "> using " + (mapperDesc ? mapperDesc : "unknown");
        }
    };
}

function addStreams() {
    var streams = Array.prototype.slice.apply(arguments);
    var i = 0;
    return {
        hasNext: function() {
            if (!streams) return false;
            var s = streams[i];
            var hasNext = s.hasNext();
            if (hasNext) return true;
            while (++i < streams.length) {
                s = streams[i];
                if (s.hasNext()) return true;
            }
            streams = null;
            return false;
        },
        next: function() {
            if (!this.hasNext()) throw "Stream Finished";
            return streams[i].next();
        },
        toString: function() {
            function mapStreamToStr(s, i) {
                return "[" + i + ":" + s + "]";
            }
            var streamsStr = streams ? streams.map(mapStreamToStr).join(", ") : "unknown streams";
            return "Composite Stream: " + streamsStr;
        }
    };
}

function streamToArray(stream, limit) {
    var arr = [];
    if ("number" === typeof limit) {
        var i = 0;
        while ((i < limit) && stream.hasNext()) {
            arr.push(stream.next());
            i++;
        }
    } else {
        while (stream.hasNext()) {
            arr.push(stream.next());
        }
    }
    return arr;
}

function arrayStream(arr) {
    var i = 0;
    var len = arr ? arr.length : 0;
    return {
        hasNext: function() {
            if (!arr) return false;
            var hasNext = (i < arr.length);
            if (hasNext) return true;
            arr = null;
            return false;
        },
        next: function() {
            if (!this.hasNext()) throw "Stream Finished";
            var _i = i;
            i++;
            return arr[_i];
        },
        toString: function() {
            return "Array Stream: length " + len;
        }
    };
}

var lower = mapStream(intStream(65, 65+26), String.fromCharCode, "fromCharCode");
var upper = mapStream(intStream(97, 97+26), String.fromCharCode, "fromCharCode");
var symbols = arrayStream(['!', '"', '£', '$', '%', '^', '&', '*', '(', ')', '-', '=']);
var stream = addStreams(lower, upper, symbols);
stream = mapStream(stream, function(it) { return "(" + it + ")"; }, "Surround with parens");
console.log(stream);
console.log("stream.toString()", ""+stream);
console.log(streamToArray(stream).join(" - "));

console.log(streamToArray(intStream(0), 100).join(" - "));