diff --git a/gradlew b/gradlew
index a69d9cb..1aa94a4 100755
--- a/gradlew
+++ b/gradlew
@@ -55,7 +55,7 @@
 #       Darwin, MinGW, and NonStop.
 #
 #   (3) This script is generated from the Groovy template
-#       https://github.com/gradle/gradle/blob/master/subprojects/plugins/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
+#       https://github.com/gradle/gradle/blob/HEAD/subprojects/plugins/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
 #       within the Gradle project.
 #
 #       You can find Gradle at https://github.com/gradle/gradle/.
@@ -80,13 +80,11 @@ do
     esac
 done
 
-APP_HOME=$( cd "${APP_HOME:-./}" && pwd -P ) || exit
-
-APP_NAME="Gradle"
+# This is normally unused
+# shellcheck disable=SC2034
 APP_BASE_NAME=${0##*/}
-
-# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
-DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+# Discard cd standard output in case $CDPATH is set (https://github.com/gradle/gradle/issues/25036)
+APP_HOME=$( cd "${APP_HOME:-./}" > /dev/null && pwd -P ) || exit
 
 # Use the maximum available, or set MAX_FD != -1 to use that value.
 MAX_FD=maximum
@@ -133,22 +131,29 @@ location of your Java installation."
     fi
 else
     JAVACMD=java
-    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+    if ! command -v java >/dev/null 2>&1
+    then
+        die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
 
 Please set the JAVA_HOME variable in your environment to match the
 location of your Java installation."
+    fi
 fi
 
 # Increase the maximum file descriptors if we can.
 if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
     case $MAX_FD in #(
       max*)
+        # In POSIX sh, ulimit -H is undefined. That's why the result is checked to see if it worked.
+        # shellcheck disable=SC2039,SC3045
         MAX_FD=$( ulimit -H -n ) ||
             warn "Could not query maximum file descriptor limit"
     esac
     case $MAX_FD in  #(
       '' | soft) :;; #(
       *)
+        # In POSIX sh, ulimit -n is undefined. That's why the result is checked to see if it worked.
+        # shellcheck disable=SC2039,SC3045
         ulimit -n "$MAX_FD" ||
             warn "Could not set maximum file descriptor limit to $MAX_FD"
     esac
@@ -193,11 +198,15 @@ if "$cygwin" || "$msys" ; then
     done
 fi
 
-# Collect all arguments for the java command;
-#   * $DEFAULT_JVM_OPTS, $JAVA_OPTS, and $GRADLE_OPTS can contain fragments of
-#     shell script including quotes and variable substitutions, so put them in
-#     double quotes to make sure that they get re-expanded; and
-#   * put everything else in single quotes, so that it's not re-expanded.
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Collect all arguments for the java command:
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, JAVA_OPTS, and optsEnvironmentVar are not allowed to contain shell fragments,
+#     and any embedded shellness will be escaped.
+#   * For example: A user cannot expect ${Hostname} to be expanded, as it is an environment variable and will be
+#     treated as '${Hostname}' itself on the command line.
 
 set -- \
         "-Dorg.gradle.appname=$APP_BASE_NAME" \
diff --git a/gradlew.bat b/gradlew.bat
index 53a6b23..6689b85 100644
--- a/gradlew.bat
+++ b/gradlew.bat
@@ -26,6 +26,7 @@ if "%OS%"=="Windows_NT" setlocal
 
 set DIRNAME=%~dp0
 if "%DIRNAME%"=="" set DIRNAME=.
+@rem This is normally unused
 set APP_BASE_NAME=%~n0
 set APP_HOME=%DIRNAME%
 
diff --git a/src/main/kotlin/blitz/Either.kt b/src/main/kotlin/blitz/Either.kt
index 6ac1760..023e5ce 100644
--- a/src/main/kotlin/blitz/Either.kt
+++ b/src/main/kotlin/blitz/Either.kt
@@ -43,12 +43,12 @@ class Either<A, B> private constructor(
 
     companion object {
         fun <A, B> ofA(a: A): Either<A, B> =
-            Either(Obj(a), null)
+            Either(Obj.of(a), null)
 
         fun <A, B> ofB(b: B): Either<A, B> =
-            Either(null, Obj(b))
+            Either(null, Obj.of(b))
     }
 }
 
-fun <A, B, R> Either<A, B>.commonize(): R where A: R, B: R =
+fun <A, B, R> Either<A, B>.flatten(): R where A: R, B: R =
     getAOrNull() ?: getB()
\ No newline at end of file
diff --git a/src/main/kotlin/blitz/Fnp.kt b/src/main/kotlin/blitz/Fnp.kt
index 34fad06..ba2713c 100644
--- a/src/main/kotlin/blitz/Fnp.kt
+++ b/src/main/kotlin/blitz/Fnp.kt
@@ -1,5 +1,7 @@
 package blitz
 
+import blitz.collections.contents
+import blitz.collections.easyMappingSequence
 import blitz.func.*
 import blitz.func.io.*
 
diff --git a/src/main/kotlin/blitz/Obj.kt b/src/main/kotlin/blitz/Obj.kt
index 2b11455..346c85f 100644
--- a/src/main/kotlin/blitz/Obj.kt
+++ b/src/main/kotlin/blitz/Obj.kt
@@ -1,11 +1,39 @@
 package blitz
 
-data class Obj<T>(val v: T)
+import blitz.async.Lock
+
+interface Obj<T> {
+    val v: T
+
+    companion object {
+        fun <T> of(v: T): Obj<T> =
+            object : Obj<T> {
+                override val v: T = v
+            }
+    }
+}
 
 fun <I, O> Obj<I>?.mapNotNull(transform: (I) -> O): Obj<O>? =
-    this?.v?.let { Obj(transform(it)) }
+    this?.v?.let { Obj.of(transform(it)) }
 
 fun <I, O> Obj<I>.map(transform: (I) -> O): Obj<O> =
-    Obj(transform(v))
+    Obj.of(transform(v))
 
-data class MutObj<T>(var v: T)
\ No newline at end of file
+interface MutObj<T> {
+    var v: T
+
+    companion object {
+        fun <T> of(v: T): MutObj<T> =
+            object : MutObj<T> {
+                override var v: T = v
+            }
+
+        fun <T> mutex(v: T): MutObj<T> =
+            object : MutObj<T> {
+                val lock = Lock()
+                override var v: T = v
+                    get() = lock.use { field }
+                    set(inp) = lock.use { field = inp }
+            }
+    }
+}
\ No newline at end of file
diff --git a/src/main/kotlin/blitz/OperationChain.kt b/src/main/kotlin/blitz/OperationChain.kt
index 584a300..f92342d 100644
--- a/src/main/kotlin/blitz/OperationChain.kt
+++ b/src/main/kotlin/blitz/OperationChain.kt
@@ -1,5 +1,7 @@
 package blitz
 
+import blitz.collections.selfInitializingSequence
+
 class OperationChain<I, O> private constructor(
     private val impl: Impl = Impl()
 ) {
diff --git a/src/main/kotlin/blitz/async/Lock.kt b/src/main/kotlin/blitz/async/Lock.kt
new file mode 100644
index 0000000..9385298
--- /dev/null
+++ b/src/main/kotlin/blitz/async/Lock.kt
@@ -0,0 +1,11 @@
+package blitz.async
+
+@JvmInline
+value class Lock private constructor(
+    private val impl: Any
+) {
+    constructor(): this(Any())
+
+    fun <R> use(block: () -> R): R =
+        synchronized(impl, block)
+}
\ No newline at end of file
diff --git a/src/main/kotlin/blitz/Batched.kt b/src/main/kotlin/blitz/collections/Batched.kt
similarity index 96%
rename from src/main/kotlin/blitz/Batched.kt
rename to src/main/kotlin/blitz/collections/Batched.kt
index 882b0d5..c9f30b6 100644
--- a/src/main/kotlin/blitz/Batched.kt
+++ b/src/main/kotlin/blitz/collections/Batched.kt
@@ -1,128 +1,128 @@
-package blitz
-
-import kotlin.math.max
-import kotlin.math.min
-
-interface BatchIterator<T>: Iterator<T> {
-    fun next(limit: Int): List<T>
-    fun next(dest: Array<T>): Int
-    fun next(dest: MutableList<T>, limit: Int)
-}
-
-interface ByteBatchIterator: BatchIterator<Byte> {
-    fun nextBytes(limit: Int): ByteArray
-
-    fun nextBytes(dest: ByteArray): Int
-}
-
-interface BatchSequence<T>: Sequence<T> {
-    override fun iterator(): BatchIterator<T>
-}
-
-interface ByteBatchSequence: BatchSequence<Byte> {
-    override fun iterator(): ByteBatchIterator
-}
-
-/**
- * Batches all get operations on the sequence.
- */
-fun <T> BatchSequence<T>.batched(count: Int): BatchSequence<T> =
-    object : BatchSequence<T> {
-        inner class Iter: BatchIterator<T> {
-            val parent = this@batched.iterator()
-
-            var batch = mutableListOf<T>()
-
-            override fun next(limit: Int): List<T> {
-                if (!hasNext())
-                    throw Exception("no next")
-
-                val c = min(limit, batch.size)
-                val ret = batch.take(c)
-                batch.removeFirst(c)
-                return ret
-            }
-
-            override fun next(dest: MutableList<T>, limit: Int) {
-                if (!hasNext())
-                    throw Exception("no next")
-
-                val c = min(limit, batch.size)
-                dest.addAll(batch.subList(0, max(0, c-1)))
-                batch.removeFirst(c)
-                return
-            }
-
-            override fun next(dest: Array<T>): Int {
-                if (!hasNext())
-                    throw Exception("no next")
-
-                val c = min(dest.size, batch.size)
-                batch.subList(0, max(0, c-1)).forEachIndexed { i, t ->
-                    dest[i] = t
-                }
-                batch.removeFirst(c)
-                return c
-            }
-
-            override fun next(): T {
-                if (!hasNext())
-                    throw Exception("no next")
-                val v = batch.first()
-                batch.removeFirst()
-                return v
-            }
-
-            override fun hasNext(): Boolean {
-                while (batch.isEmpty()) {
-                    if (!parent.hasNext())
-                        return false
-                    parent.next(batch, count)
-                }
-                return true
-            }
-        }
-
-        override fun iterator(): BatchIterator<T> =
-            Iter()
-    }
-
-fun <T> Sequence<T>.asBatch(): BatchSequence<T> =
-    object : BatchSequence<T> {
-        inner class Iter: BatchIterator<T> {
-            var iter = this@asBatch.iterator()
-
-            override fun next(limit: Int): List<T> =
-                mutableListOf<T>()
-                    .also { next(it, limit) }
-
-            override fun next(dest: MutableList<T>, limit: Int) {
-                for (i in 0..<limit) {
-                    if (!iter.hasNext())
-                        break
-                    dest.add(iter.next())
-                }
-            }
-
-            override fun next(dest: Array<T>): Int {
-                var i = 0
-                while (i < dest.size) {
-                    if (!iter.hasNext())
-                        break
-                    dest[i ++] = iter.next()
-                }
-                return i
-            }
-
-            override fun next(): T {
-                return iter.next()
-            }
-
-            override fun hasNext(): Boolean {
-                return iter.hasNext()
-            }
-        }
-
-        override fun iterator(): BatchIterator<T> =
-            Iter()
+package blitz.collections
+
+import kotlin.math.max
+import kotlin.math.min
+
+interface BatchIterator<T>: Iterator<T> {
+    fun next(limit: Int): List<T>
+    fun next(dest: Array<T>): Int
+    fun next(dest: MutableList<T>, limit: Int)
+}
+
+interface ByteBatchIterator: BatchIterator<Byte> {
+    fun nextBytes(limit: Int): ByteArray
+
+    fun nextBytes(dest: ByteArray): Int
+}
+
+interface BatchSequence<T>: Sequence<T> {
+    override fun iterator(): BatchIterator<T>
+}
+
+interface ByteBatchSequence: BatchSequence<Byte> {
+    override fun iterator(): ByteBatchIterator
+}
+
+/**
+ * Batches all get operations on the sequence.
+ */
+fun <T> BatchSequence<T>.batched(count: Int): BatchSequence<T> =
+    object : BatchSequence<T> {
+        inner class Iter: BatchIterator<T> {
+            val parent = this@batched.iterator()
+
+            var batch = mutableListOf<T>()
+
+            override fun next(limit: Int): List<T> {
+                if (!hasNext())
+                    throw Exception("no next")
+
+                val c = min(limit, batch.size)
+                val ret = batch.take(c)
+                batch.removeFirst(c)
+                return ret
+            }
+
+            override fun next(dest: MutableList<T>, limit: Int) {
+                if (!hasNext())
+                    throw Exception("no next")
+
+                val c = min(limit, batch.size)
+                dest.addAll(batch.subList(0, max(0, c-1)))
+                batch.removeFirst(c)
+                return
+            }
+
+            override fun next(dest: Array<T>): Int {
+                if (!hasNext())
+                    throw Exception("no next")
+
+                val c = min(dest.size, batch.size)
+                batch.subList(0, max(0, c-1)).forEachIndexed { i, t ->
+                    dest[i] = t
+                }
+                batch.removeFirst(c)
+                return c
+            }
+
+            override fun next(): T {
+                if (!hasNext())
+                    throw Exception("no next")
+                val v = batch.first()
+                batch.removeFirst()
+                return v
+            }
+
+            override fun hasNext(): Boolean {
+                while (batch.isEmpty()) {
+                    if (!parent.hasNext())
+                        return false
+                    parent.next(batch, count)
+                }
+                return true
+            }
+        }
+
+        override fun iterator(): BatchIterator<T> =
+            Iter()
+    }
+
+fun <T> Sequence<T>.asBatch(): BatchSequence<T> =
+    object : BatchSequence<T> {
+        inner class Iter: BatchIterator<T> {
+            var iter = this@asBatch.iterator()
+
+            override fun next(limit: Int): List<T> =
+                mutableListOf<T>()
+                    .also { next(it, limit) }
+
+            override fun next(dest: MutableList<T>, limit: Int) {
+                for (i in 0..<limit) {
+                    if (!iter.hasNext())
+                        break
+                    dest.add(iter.next())
+                }
+            }
+
+            override fun next(dest: Array<T>): Int {
+                var i = 0
+                while (i < dest.size) {
+                    if (!iter.hasNext())
+                        break
+                    dest[i ++] = iter.next()
+                }
+                return i
+            }
+
+            override fun next(): T {
+                return iter.next()
+            }
+
+            override fun hasNext(): Boolean {
+                return iter.hasNext()
+            }
+        }
+
+        override fun iterator(): BatchIterator<T> =
+            Iter()
     }
\ No newline at end of file
diff --git a/src/main/kotlin/blitz/BatchedUtils.kt b/src/main/kotlin/blitz/collections/BatchedUtils.kt
similarity index 89%
rename from src/main/kotlin/blitz/BatchedUtils.kt
rename to src/main/kotlin/blitz/collections/BatchedUtils.kt
index f6e2f61..f337239 100644
--- a/src/main/kotlin/blitz/BatchedUtils.kt
+++ b/src/main/kotlin/blitz/collections/BatchedUtils.kt
@@ -1,10 +1,10 @@
-package blitz
-
-fun ByteBatchSequence.stringify(batch: Int = 64): Sequence<String> {
-    val iter = iterator()
-    return generateSequence {
-        if (iter.hasNext())
-            iter.nextBytes(batch).decodeToString()
-        else null
-    }
+package blitz.collections
+
+fun ByteBatchSequence.stringify(batch: Int = 64): Sequence<String> {
+    val iter = iterator()
+    return generateSequence {
+        if (iter.hasNext())
+            iter.nextBytes(batch).decodeToString()
+        else null
+    }
 }
\ No newline at end of file
diff --git a/src/main/kotlin/blitz/Contents.kt b/src/main/kotlin/blitz/collections/Contents.kt
similarity index 94%
rename from src/main/kotlin/blitz/Contents.kt
rename to src/main/kotlin/blitz/collections/Contents.kt
index 9b91d54..2151f22 100644
--- a/src/main/kotlin/blitz/Contents.kt
+++ b/src/main/kotlin/blitz/collections/Contents.kt
@@ -1,52 +1,51 @@
-package blitz
-
-class Contents<T> internal constructor(
-    private val iterable: Iterable<T>
-): Iterable<T> {
-    override fun iterator(): Iterator<T> =
-        iterable.iterator()
-
-    override fun equals(other: Any?): Boolean {
-        if (other !is Contents<*>)
-            return false
-
-        val it1 = this.iterable.iterator()
-        val it2 = other.iterable.iterator()
-
-        while (true) {
-            val hasNext1 = it1.hasNext()
-            val hasNext2 = it2.hasNext()
-
-            if ((hasNext1 && !hasNext2) || (hasNext2 && !hasNext1))
-                return false
-
-            if (!hasNext1)
-                return true
-
-            if (it1.next() != it2.next())
-                return false
-        }
-    }
-
-    override fun hashCode(): Int =
-        iterable.hashCode()
-
-    override fun toString(): String =
-        joinToString(
-            separator = ", ",
-            prefix = "[",
-            postfix = "]"
-        ) {
-            it.toString()
-        }
-}
-
-
-val <T> Iterable<T>.contents get() =
-    Contents(this)
-
-val <T> Sequence<T>.contents get() =
-    Contents(this.asIterable())
-
-val <T> Array<T>.contents get() =
+package blitz.collections
+
+class Contents<T> internal constructor(
+    private val iterable: Iterable<T>
+): Iterable<T> {
+    override fun iterator(): Iterator<T> =
+        iterable.iterator()
+
+    override fun equals(other: Any?): Boolean {
+        if (other !is Contents<*>)
+            return false
+
+        val it1 = this.iterable.iterator()
+        val it2 = other.iterable.iterator()
+
+        while (true) {
+            val hasNext1 = it1.hasNext()
+            val hasNext2 = it2.hasNext()
+
+            if ((hasNext1 && !hasNext2) || (hasNext2 && !hasNext1))
+                return false
+
+            if (!hasNext1)
+                return true
+
+            if (it1.next() != it2.next())
+                return false
+        }
+    }
+
+    override fun hashCode(): Int =
+        iterable.hashCode()
+
+    override fun toString(): String =
+        joinToString(
+            separator = ", ",
+            prefix = "[",
+            postfix = "]"
+        ) {
+            it.toString()
+        }
+}
+
+val <T> Iterable<T>.contents get() =
+    Contents(this)
+
+val <T> Sequence<T>.contents get() =
+    Contents(this.asIterable())
+
+val <T> Array<T>.contents get() =
     Contents(this.asIterable())
\ No newline at end of file
diff --git a/src/main/kotlin/blitz/ListOps.kt b/src/main/kotlin/blitz/collections/ListOps.kt
similarity index 88%
rename from src/main/kotlin/blitz/ListOps.kt
rename to src/main/kotlin/blitz/collections/ListOps.kt
index 598cbd0..dda896f 100644
--- a/src/main/kotlin/blitz/ListOps.kt
+++ b/src/main/kotlin/blitz/collections/ListOps.kt
@@ -1,13 +1,13 @@
-package blitz
-
-fun <T> MutableList<T>.removeFirst(count: Int) {
-    repeat(count) {
-        removeFirst()
-    }
-}
-
-fun <T> MutableList<T>.removeLast(count: Int) {
-    repeat(count) {
-        removeLast()
-    }
+package blitz.collections
+
+fun <T> MutableList<T>.removeFirst(count: Int) {
+    repeat(count) {
+        removeFirst()
+    }
+}
+
+fun <T> MutableList<T>.removeLast(count: Int) {
+    repeat(count) {
+        removeLast()
+    }
 }
\ No newline at end of file
diff --git a/src/main/kotlin/blitz/SequenceBase.kt b/src/main/kotlin/blitz/collections/SequenceBase.kt
similarity index 95%
rename from src/main/kotlin/blitz/SequenceBase.kt
rename to src/main/kotlin/blitz/collections/SequenceBase.kt
index c8899df..031bde1 100644
--- a/src/main/kotlin/blitz/SequenceBase.kt
+++ b/src/main/kotlin/blitz/collections/SequenceBase.kt
@@ -1,42 +1,42 @@
-package blitz
-
-interface IndexableSequence<T>: Sequence<T> {
-    operator fun get(index: Int): T
-}
-
-fun <T> IndexableSequence<T>.modifier(mod: (Sequence<T>) -> Sequence<T>) =
-    object : IndexableSequence<T> {
-        val other = mod(this@modifier)
-
-        override fun iterator(): Iterator<T> =
-            other.iterator()
-
-        override fun get(index: Int): T =
-            this@modifier[index]
-    }
-
-fun <T> Sequence<T>.asIndexable(): IndexableSequence<T> =
-    object : IndexableSequence<T> {
-        val iter = this@asIndexable.iterator()
-        val values = mutableListOf<T>()
-
-        override fun get(index: Int): T {
-            if (index >= values.size) {
-                repeat(index + 1 - values.size) {
-                    values.add(iter.next())
-                }
-            }
-            return values[index]
-        }
-
-        override fun iterator(): Iterator<T> =
-            object : Iterator<T> {
-                var i = 0
-
-                override fun hasNext(): Boolean =
-                    i < values.size || iter.hasNext()
-
-                override fun next(): T =
-                    get(i ++)
-            }
+package blitz.collections
+
+interface IndexableSequence<T>: Sequence<T> {
+    operator fun get(index: Int): T
+}
+
+fun <T> IndexableSequence<T>.modifier(mod: (Sequence<T>) -> Sequence<T>) =
+    object : IndexableSequence<T> {
+        val other = mod(this@modifier)
+
+        override fun iterator(): Iterator<T> =
+            other.iterator()
+
+        override fun get(index: Int): T =
+            this@modifier[index]
+    }
+
+fun <T> Sequence<T>.asIndexable(): IndexableSequence<T> =
+    object : IndexableSequence<T> {
+        val iter = this@asIndexable.iterator()
+        val values = mutableListOf<T>()
+
+        override fun get(index: Int): T {
+            if (index >= values.size) {
+                repeat(index + 1 - values.size) {
+                    values.add(iter.next())
+                }
+            }
+            return values[index]
+        }
+
+        override fun iterator(): Iterator<T> =
+            object : Iterator<T> {
+                var i = 0
+
+                override fun hasNext(): Boolean =
+                    i < values.size || iter.hasNext()
+
+                override fun next(): T =
+                    get(i ++)
+            }
     }
\ No newline at end of file
diff --git a/src/main/kotlin/blitz/SequenceCreators.kt b/src/main/kotlin/blitz/collections/SequenceCreators.kt
similarity index 93%
rename from src/main/kotlin/blitz/SequenceCreators.kt
rename to src/main/kotlin/blitz/collections/SequenceCreators.kt
index 958fafa..ff330b2 100644
--- a/src/main/kotlin/blitz/SequenceCreators.kt
+++ b/src/main/kotlin/blitz/collections/SequenceCreators.kt
@@ -1,75 +1,77 @@
-package blitz
-
-import kotlin.math.max
-
-fun <T> lazySequence(vararg init: Pair<Int, T>, default: Obj<T>?, f: (Int, (Int) -> T) -> T): IndexableSequence<T> =
-    object : IndexableSequence<T> {
-        val map = mutableMapOf(*init)
-
-        var current: Int? = null
-
-        fun comp(iIn: Int): T {
-            val i = max(0, iIn)
-            if (current == i)
-                return (default ?: throw Exception("recursion detected")).v
-            return map[i] ?: let {
-                current = i
-                val res = f(i, ::comp)
-                map[i] = res
-                current = null
-                res
-            }
-        }
-
-        override fun get(index: Int) = comp(index)
-
-        override fun iterator(): Iterator<T> =
-            object : Iterator<T> {
-                override fun hasNext() = true
-
-                private var i = 0
-
-                override fun next(): T =
-                    comp(i ++)
-            }
-    }
-
-fun <T> easySequence(vararg init: Pair<Int, T?>, f: (Int, (Int) -> T?) -> T?): Sequence<T?> =
-    lazySequence(*init, default = Obj(null)) { i, ff ->
-        f(i) { index ->
-            var indexC = index
-            var v: T? = null
-            while (indexC > 0 && v == null)
-                v = ff(indexC --)
-            v
-        }
-    }
-
-fun <I, T> Sequence<I>.easyMappingSequence(
-    vararg init: Pair<Int, T?>,
-    f: (Int, (Int) -> T?, (Int) -> I) -> T?
-): Sequence<T?> {
-    val indexable = this.asIndexable()
-    return easySequence(*init) { i, ff ->
-        f(i, ff, indexable::get)
-    }.limitBy(indexable)
-        .removeNull()
-}
-
-fun <T> selfInitializingSequence(block: Provider<Sequence<T>>): Sequence<T> =
-    object : Sequence<T> {
-        val seq by lazy(block)
-
-        inner class Iter : Iterator<T> {
-            val iter = seq.iterator()
-
-            override fun hasNext(): Boolean =
-                iter.hasNext()
-
-            override fun next(): T =
-                iter.next()
-        }
-
-        override fun iterator(): Iterator<T> =
-            Iter()
+package blitz.collections
+
+import blitz.Obj
+import blitz.Provider
+import kotlin.math.max
+
+fun <T> lazySequence(vararg init: Pair<Int, T>, default: Obj<T>?, f: (Int, (Int) -> T) -> T): IndexableSequence<T> =
+    object : IndexableSequence<T> {
+        val map = mutableMapOf(*init)
+
+        var current: Int? = null
+
+        fun comp(iIn: Int): T {
+            val i = max(0, iIn)
+            if (current == i)
+                return (default ?: throw Exception("recursion detected")).v
+            return map[i] ?: let {
+                current = i
+                val res = f(i, ::comp)
+                map[i] = res
+                current = null
+                res
+            }
+        }
+
+        override fun get(index: Int) = comp(index)
+
+        override fun iterator(): Iterator<T> =
+            object : Iterator<T> {
+                override fun hasNext() = true
+
+                private var i = 0
+
+                override fun next(): T =
+                    comp(i ++)
+            }
+    }
+
+fun <T> easySequence(vararg init: Pair<Int, T?>, f: (Int, (Int) -> T?) -> T?): Sequence<T?> =
+    lazySequence(*init, default = Obj.of(null)) { i, ff ->
+        f(i) { index ->
+            var indexC = index
+            var v: T? = null
+            while (indexC > 0 && v == null)
+                v = ff(indexC --)
+            v
+        }
+    }
+
+fun <I, T> Sequence<I>.easyMappingSequence(
+    vararg init: Pair<Int, T?>,
+    f: (Int, (Int) -> T?, (Int) -> I) -> T?
+): Sequence<T?> {
+    val indexable = this.asIndexable()
+    return easySequence(*init) { i, ff ->
+        f(i, ff, indexable::get)
+    }.limitBy(indexable)
+        .removeNull()
+}
+
+fun <T> selfInitializingSequence(block: Provider<Sequence<T>>): Sequence<T> =
+    object : Sequence<T> {
+        val seq by lazy(block)
+
+        inner class Iter : Iterator<T> {
+            val iter = seq.iterator()
+
+            override fun hasNext(): Boolean =
+                iter.hasNext()
+
+            override fun next(): T =
+                iter.next()
+        }
+
+        override fun iterator(): Iterator<T> =
+            Iter()
     }
\ No newline at end of file
diff --git a/src/main/kotlin/blitz/SequenceOps.kt b/src/main/kotlin/blitz/collections/SequenceOps.kt
similarity index 95%
rename from src/main/kotlin/blitz/SequenceOps.kt
rename to src/main/kotlin/blitz/collections/SequenceOps.kt
index e747cb7..2282b13 100644
--- a/src/main/kotlin/blitz/SequenceOps.kt
+++ b/src/main/kotlin/blitz/collections/SequenceOps.kt
@@ -1,25 +1,25 @@
-package blitz
-
-fun <T> Sequence<T>.removeNull(): Sequence<T> =
-    mapNotNull { it }
-
-fun <T> IndexableSequence<T>.removeNull(): IndexableSequence<T> =
-    modifier { it.removeNull() }
-
-fun <A, B> Sequence<A>.limitBy(other: Sequence<B>): Sequence<A> =
-    object : Sequence<A> {
-        override fun iterator(): Iterator<A> =
-            object : Iterator<A> {
-                val s = this@limitBy.iterator()
-                val o = other.iterator()
-
-                override fun hasNext(): Boolean =
-                    o.hasNext() && s.hasNext()
-
-                override fun next(): A =
-                    s.next().also { o.next() }
-            }
-    }
-
-fun <A, B> IndexableSequence<A>.limitBy(other: Sequence<B>): IndexableSequence<A> =
+package blitz.collections
+
+fun <T> Sequence<T>.removeNull(): Sequence<T> =
+    mapNotNull { it }
+
+fun <T> IndexableSequence<T>.removeNull(): IndexableSequence<T> =
+    modifier { it.removeNull() }
+
+fun <A, B> Sequence<A>.limitBy(other: Sequence<B>): Sequence<A> =
+    object : Sequence<A> {
+        override fun iterator(): Iterator<A> =
+            object : Iterator<A> {
+                val s = this@limitBy.iterator()
+                val o = other.iterator()
+
+                override fun hasNext(): Boolean =
+                    o.hasNext() && s.hasNext()
+
+                override fun next(): A =
+                    s.next().also { o.next() }
+            }
+    }
+
+fun <A, B> IndexableSequence<A>.limitBy(other: Sequence<B>): IndexableSequence<A> =
     modifier { it.limitBy(other) }
\ No newline at end of file
diff --git a/src/main/kotlin/blitz/func/Utils.kt b/src/main/kotlin/blitz/func/Utils.kt
index 529ba40..e8a8a5b 100644
--- a/src/main/kotlin/blitz/func/Utils.kt
+++ b/src/main/kotlin/blitz/func/Utils.kt
@@ -1,7 +1,7 @@
 package blitz.func
 
-import blitz.ByteBatchSequence
-import blitz.stringify
+import blitz.collections.ByteBatchSequence
+import blitz.collections.stringify
 
 fun <T> Monad<Sequence<Sequence<T>>>.flatten(): Monad<Sequence<T>> =
     bind { it.flatten() }
diff --git a/src/main/kotlin/blitz/func/io/File.kt b/src/main/kotlin/blitz/func/io/File.kt
index 69c8d02..d1d4f28 100644
--- a/src/main/kotlin/blitz/func/io/File.kt
+++ b/src/main/kotlin/blitz/func/io/File.kt
@@ -1,6 +1,6 @@
 package blitz.func.io
 
-import blitz.*
+import blitz.collections.ByteBatchSequence
 import blitz.func.*
 import blitz.io.*
 
diff --git a/src/main/kotlin/blitz/io/File.kt b/src/main/kotlin/blitz/io/File.kt
index dfbddd8..26471a7 100644
--- a/src/main/kotlin/blitz/io/File.kt
+++ b/src/main/kotlin/blitz/io/File.kt
@@ -1,6 +1,6 @@
 package blitz.io
 
-import blitz.ByteBatchSequence
+import blitz.collections.ByteBatchSequence
 import kotlinx.io.Buffer
 import kotlinx.io.files.SystemFileSystem
 
diff --git a/src/main/kotlin/blitz/io/Raw.kt b/src/main/kotlin/blitz/io/Raw.kt
index 7ee063a..8d09840 100644
--- a/src/main/kotlin/blitz/io/Raw.kt
+++ b/src/main/kotlin/blitz/io/Raw.kt
@@ -2,8 +2,8 @@ package blitz.io
 
 import kotlinx.io.RawSource
 import kotlinx.io.buffered
-import blitz.ByteBatchIterator
-import blitz.ByteBatchSequence
+import blitz.collections.ByteBatchIterator
+import blitz.collections.ByteBatchSequence
 import blitz.Provider
 
 fun Provider<RawSource>.readerSequence(): ByteBatchSequence =