Can now parse TAR files.

21 files changed, 1006 insertions, 137 deletions

diff --git a/documentation/research/Agent.md b/documentation/research/Agent.md
new file mode 100644
index 000000000..5f8a7629a
--- /dev/null
+++ b/documentation/research/Agent.md
@@ -0,0 +1,8 @@
+# Reference
+
+1. [Introduction to Java Agents](https://devolution.tech/introduction-to-java-agents/)
+1. https://docs.oracle.com/javase/7/docs/api/java/lang/instrument/package-summary.html
+1. http://javabeat.net/introduction-to-java-agents/
+1. https://www.javacodegeeks.com/2015/09/java-agents.html
+1. https://github.com/cretz/stackparam
+
diff --git a/documentation/research/Memory Management.md b/documentation/research/Memory Management.md
index 7b326a4a0..8905c6b20 100644
--- a/documentation/research/Memory Management.md
+++ b/documentation/research/Memory Management.md
@@ -26,6 +26,7 @@
 
 # Reference
 
+1. [Relative Pointers](https://www.gingerbill.org/article/2020/05/17/relative-pointers/)
 1. [Scopes Describe Frames: A Uniform Model for Memory Layout in Dynamic Semantics](http://drops.dagstuhl.de/opus/volltexte/2016/6114/)
 1. https://uridiumauthor.blogspot.com/2018/06/memory-management.html
 1. https://github.com/mtrebi/memory-allocators
diff --git a/documentation/research/Optics (eg lenses & prisms).md b/documentation/research/Optics (eg lenses & prisms).md
index 493b05c61..6f7acb5ca 100644
--- a/documentation/research/Optics (eg lenses & prisms).md
+++ b/documentation/research/Optics (eg lenses & prisms).md
@@ -1,5 +1,6 @@
 # Reference
 
+1. [Profunctor optics, a categorical update](https://arxiv.org/abs/2001.07488)
 1. [On Lawful Lenses](https://blog.statebox.org/on-lawful-lenses-6e18a1e17bdf)
 1. https://medium.com/urbint-engineering/haskell-lens-operator-onboarding-a235481e8fac
 1. https://fstarlang.github.io/general/2018/01/12/lens-indexed-lenses.html
diff --git a/documentation/research/Optimization.md b/documentation/research/Optimization.md
index a99b474e3..1fac9193b 100644
--- a/documentation/research/Optimization.md
+++ b/documentation/research/Optimization.md
@@ -8,6 +8,7 @@
 
 # Reference
 
+1. [A Language for Describing Optimization Strategies](https://arxiv.org/abs/2002.02268)
 1. https://docs.google.com/presentation/d/1tpeJZFObkeick4CF-mx0L3CeCgvT15B96aJeRpxEPcE/preview?slide=id.p
 1. https://www.quora.com/What-is-the-future-of-optimizing-compilers?share=1
 1. https://advancedweb.hu/2016/05/27/jvm_jit_optimization_techniques/ &&& https://advancedweb.hu/2016/06/28/jvm_jit_optimization_techniques_part_2/
diff --git a/documentation/research/math.md b/documentation/research/math.md
index 777a3c1d2..91c434dca 100644
--- a/documentation/research/math.md
+++ b/documentation/research/math.md
@@ -160,6 +160,8 @@
 
 # Geometric Algebra | Clifford Algebra
 
+1. [Siggraph2019 Geometric Algebra](https://www.youtube.com/watch?v=tX4H_ctggYo)
+1. [Introduction to Clifford Algebra](https://www.av8n.com/physics/clifford-intro.htm)
 1. [An Introduction to Geometric Algebra over R^2](https://bitworking.org/news/ga/2d)
 1. [Exterior Product](https://medium.com/@marksaroufim/exterior-product-ecd5836c28ab)
 1. [Projective geometric algebra: A modern framework for doing geometry](http://page.math.tu-berlin.de/~gunn/PGA/index.html)
diff --git a/documentation/research/operating_system.md b/documentation/research/operating_system.md
index c21f82f5b..82943f024 100644
--- a/documentation/research/operating_system.md
+++ b/documentation/research/operating_system.md
@@ -19,6 +19,7 @@
 
 ## Operating system
 
+1. [CLOSOS: Specication of a Lisp operating system.](http://metamodular.com/lispos.pdf)
 1. [CLOSOS: Specication of a Lisp operating system.](http://metamodular.com/closos.pdf)
 1. https://medium.com/@jasonyuan/introducing-mercury-os-f4de45a04289
 1. http://lsneff.me/why-nebulet/ ||| https://github.com/nebulet/nebulet
diff --git a/documentation/research/text_editor & ide.md b/documentation/research/text_editor & ide.md
index 3d234605f..ab5f3f4fe 100644
--- a/documentation/research/text_editor & ide.md
+++ b/documentation/research/text_editor & ide.md
@@ -204,6 +204,7 @@
 
 ## Structured editing
 
+1. [Going beyond regular expressions with structural code search](https://about.sourcegraph.com/blog/going-beyond-regular-expressions-with-structural-code-search)
 1. [俺のlisp](https://github.com/illiichi/orenolisp)
 1. [豆腐 (Tofu): meaningful code editing](https://gregoor.github.io/tofu/)
 1. [Tiled Text](http://www.tiledtext.com/projects/tiledtext)
diff --git a/stdlib/source/lux/abstract/monad/free.lux b/stdlib/source/lux/abstract/monad/free.lux
index 214261450..5194963b4 100644
--- a/stdlib/source/lux/abstract/monad/free.lux
+++ b/stdlib/source/lux/abstract/monad/free.lux
@@ -1,5 +1,5 @@
 (.module:
-  lux
+  [lux #*]
   [///
    [functor (#+ Functor)]
    [apply (#+ Apply)]
diff --git a/stdlib/source/lux/control/parser.lux b/stdlib/source/lux/control/parser.lux
index 88eefcdaf..d854be6d0 100644
--- a/stdlib/source/lux/control/parser.lux
+++ b/stdlib/source/lux/control/parser.lux
@@ -92,29 +92,28 @@
     (-> (Parser s a) s (Try [s a])))
   (p input))
 
-(def: #export (some p)
+(def: #export (some parser)
   {#.doc "0-or-more combinator."}
   (All [s a]
     (-> (Parser s a) (Parser s (List a))))
   (function (_ input)
-    (case (p input)
+    (case (parser input)
       (#try.Failure _)
       (#try.Success [input (list)])
 
-      (#try.Success [input' x])
-      (run (do ..monad
-             [xs (some p)]
-             (wrap (list& x xs)))
+      (#try.Success [input' head])
+      (run (:: ..monad map (|>> (list& head))
+               (some parser))
            input'))))
 
-(def: #export (many p)
+(def: #export (many parser)
   {#.doc "1-or-more combinator."}
   (All [s a]
     (-> (Parser s a) (Parser s (List a))))
-  (do ..monad
-    [x p
-     xs (some p)]
-    (wrap (list& x xs))))
+  (do {@ ..monad}
+    [head parser]
+    (:: @ map (|>> (list& head))
+        (some parser))))
 
 (def: #export (and p1 p2)
   {#.doc "Sequencing combinator."}
@@ -289,7 +288,17 @@
       (#try.Success [input' _])
       (#try.Success [input' true]))))
 
-(def: #export (codec Codec<a,z> parser)
+(def: #export (speculative parser)
+  (All [s a] (-> (Parser s a) (Parser s a)))
+  (function (_ input)
+    (case (parser input)
+      (#try.Success [input' output])
+      (#try.Success [input output])
+
+      output
+      output)))
+
+(def: #export (codec codec parser)
   (All [s a z] (-> (Codec a z) (Parser s a) (Parser s z)))
   (function (_ input)
     (case (parser input)
@@ -297,7 +306,7 @@
       (#try.Failure error)
 
       (#try.Success [input' to-decode])
-      (case (:: Codec<a,z> decode to-decode)
+      (case (:: codec decode to-decode)
         (#try.Failure error)
         (#try.Failure error)
         
diff --git a/stdlib/source/lux/control/parser/binary.lux b/stdlib/source/lux/control/parser/binary.lux
index b2a1b1b52..3dc061940 100644
--- a/stdlib/source/lux/control/parser/binary.lux
+++ b/stdlib/source/lux/control/parser/binary.lux
@@ -8,7 +8,7 @@
     ["." try (#+ Try)]
     ["." exception (#+ exception:)]]
    [data
-    ["." binary (#+ Binary)]
+    ["/" binary (#+ Binary)]
     [number
      ["n" nat]
      ["." frac]]
@@ -40,11 +40,21 @@
     (#try.Failure msg)
     
     (#try.Success [[end _] output])
-    (let [length (binary.size input)]
+    (let [length (/.size input)]
       (if (n.= end length)
         (#try.Success output)
         (exception.throw ..binary-was-not-fully-read [length end])))))
 
+(def: #export end?
+  (Parser Bit)
+  (function (_ (^@ input [offset data]))
+    (#try.Success [input (n.= offset (/.size data))])))
+
+(def: #export remaining
+  (Parser Nat)
+  (function (_ (^@ input [offset data]))
+    (#try.Success [input (n.- offset (/.size data))])))
+
 (type: #export Size Nat)
 
 (def: #export size/8 Size 1)
@@ -63,10 +73,10 @@
          (#try.Failure error)
          (#try.Failure error))))]
 
-  [bits/8  ..size/8  binary.read/8]
-  [bits/16 ..size/16 binary.read/16]
-  [bits/32 ..size/32 binary.read/32]
-  [bits/64 ..size/64 binary.read/64]
+  [bits/8  ..size/8  /.read/8]
+  [bits/16 ..size/16 /.read/16]
+  [bits/32 ..size/32 /.read/32]
+  [bits/64 ..size/64 /.read/64]
   )
 
 (template [<name> <type>]
@@ -126,23 +136,27 @@
       1 (wrap #1)
       _ (//.lift (exception.throw ..not-a-bit [value])))))
 
-(template [<name> <bits> <size>]
+(def: #export (segment size)
+  (-> Nat (Parser Binary))
+  (function (_ [offset binary])
+    (case size
+      0 (#try.Success [[offset binary] (/.create 0)])
+      _ (do try.monad
+          [#let [end (n.+ size offset)]
+           output (/.slice offset (.dec end) binary)]
+          (wrap [[end binary] output])))))
+
+(template [<name> <bits>]
   [(def: #export <name>
      (Parser Binary)
      (do //.monad
        [size (//@map .nat <bits>)]
-       (function (_ [offset binary])
-         (case size
-           0 (#try.Success [[offset binary] (binary.create 0)])
-           _ (do try.monad
-               [#let [end (n.+ size offset)]
-                output (binary.slice offset (.dec end) binary)]
-               (wrap [[end binary] output]))))))]
-
-  [binary/8  ..bits/8  ..size/8]
-  [binary/16 ..bits/16 ..size/16]
-  [binary/32 ..bits/32 ..size/32]
-  [binary/64 ..bits/64 ..size/64]
+       (..segment size)))]
+
+  [binary/8  ..bits/8]
+  [binary/16 ..bits/16]
+  [binary/32 ..bits/32]
+  [binary/64 ..bits/64]
   )
 
 (template [<name> <binary>]
@@ -160,7 +174,7 @@
 
 (def: #export text ..utf8/64)
 
-(template [<name> <bits> <size>]
+(template [<name> <bits>]
   [(def: #export (<name> valueP)
      (All [v] (-> (Parser v) (Parser (Row v))))
      (do //.monad
@@ -179,10 +193,10 @@
                     (row.add value output)))
            (//@wrap output)))))]
 
-  [row/8  ..bits/8  ..size/8]
-  [row/16 ..bits/16 ..size/16]
-  [row/32 ..bits/32 ..size/32]
-  [row/64 ..bits/64 ..size/64]
+  [row/8  ..bits/8]
+  [row/16 ..bits/16]
+  [row/32 ..bits/32]
+  [row/64 ..bits/64]
   )
 
 (def: #export maybe
diff --git a/stdlib/source/lux/data/binary.lux b/stdlib/source/lux/data/binary.lux
index defb62049..3853e6aa5 100644
--- a/stdlib/source/lux/data/binary.lux
+++ b/stdlib/source/lux/data/binary.lux
@@ -219,7 +219,9 @@
       (#try.Success binary))
     (exception.throw ..index-out-of-bounds [(..!size binary) idx])))
 
-(structure: #export equivalence (Equivalence Binary)
+(structure: #export equivalence
+  (Equivalence Binary)
+  
   (def: (= reference sample)
     (`` (for {(~~ (static @.old))
               (java/util/Arrays::equals reference sample)
diff --git a/stdlib/source/lux/data/format/tar.lux b/stdlib/source/lux/data/format/tar.lux
index a9bb06954..42e8103e7 100644
--- a/stdlib/source/lux/data/format/tar.lux
+++ b/stdlib/source/lux/data/format/tar.lux
@@ -9,6 +9,7 @@
     ["<>" parser
      ["<b>" binary (#+ Parser)]]]
    [data
+    ["." product]
     ["." binary (#+ Binary)]
     ["." text (#+ Char)
      ["%" format (#+ format)]
@@ -48,31 +49,33 @@
 (def: small-size Size 6)
 (def: big-size Size 11)
 
-(template [<exception> <maximum> <size>
+(template [<exception> <limit> <size>
            <type> <in> <out> <writer> <suffix>
            <coercion>]
-  [(def: <maximum>
+  [(def: #export <limit>
+     Nat
      (|> ..octal-size
          (list.repeat <size>)
-         (list@fold n.* 1)))
+         (list@fold n.* 1)
+         inc))
 
    (exception: #export (<exception> {value Nat})
      (exception.report
       ["Value" (%.nat value)]
-      ["Maximum" (%.nat <maximum>)]))
+      ["Maximum" (%.nat (dec <limit>))]))
 
-   (abstract: <type>
+   (abstract: #export <type>
      {}
 
      Nat
 
      (def: #export (<in> value)
        (-> Nat (Try <type>))
-       (if (|> value (n.% <maximum>) (n.= value))
+       (if (|> value (n.% <limit>) (n.= value))
          (#try.Success (:abstraction value))
          (exception.throw <exception> [value])))
 
-     (def: <out>
+     (def: #export <out>
        (-> <type> Nat)
        (|>> :representation))
 
@@ -89,25 +92,74 @@
 
      (def: <coercion>
        (-> Nat <type>)
-       (|>> (n.% <maximum>)
+       (|>> (n.% <limit>)
             :abstraction))
      )]
 
-  [not-a-small-number maximum-small-size ..small-size
+  [not-a-small-number small-limit ..small-size
    Small small from-small
    small-writer (format ..blank ..null)
    coerce-small]
-  [not-a-big-number maximum-big-size ..big-size
+  [not-a-big-number big-limit ..big-size
    Big big from-big
    big-writer ..blank
    coerce-big]
   )
 
+(exception: #export (wrong-character {expected Char} {actual Char})
+  (exception.report
+   ["Expected" (%.nat expected)]
+   ["Actual" (%.nat actual)]))
+
+(def: verify-small-suffix
+  (Parser Any)
+  (do <>.monad
+    [pre-end <b>.bits/8
+     end <b>.bits/8
+     _ (let [expected (`` (char (~~ (static ..blank))))]
+         (<>.assert (exception.construct ..wrong-character [expected pre-end])
+                    (n.= expected pre-end)))
+     _ (let [expected (`` (char (~~ (static ..null))))]
+         (<>.assert (exception.construct ..wrong-character [expected end])
+                    (n.= expected end)))]
+    (wrap [])))
+
+(def: small-parser
+  (Parser Small)
+  (do <>.monad
+    [digits (<b>.segment ..small-size)
+     digits (<>.lift
+             (encoding.from-utf8 digits))
+     _ ..verify-small-suffix]
+    (<>.lift
+     (do {@ try.monad}
+       [value (:: n.octal decode digits)]
+       (..small value)))))
+
+(def: big-parser
+  (Parser Big)
+  (do <>.monad
+    [digits (<b>.segment ..big-size)
+     digits (<>.lift
+             (encoding.from-utf8 digits))
+     end <b>.bits/8
+     _ (let [expected (`` (char (~~ (static ..blank))))]
+         (<>.assert (exception.construct ..wrong-character [expected end])
+                    (n.= expected end)))]
+    (<>.lift
+     (do {@ try.monad}
+       [value (:: n.octal decode digits)]
+       (..big value)))))
+
 (abstract: Checksum
   {}
 
   Text
 
+  (def: from-checksum
+    (-> Checksum Text)
+    (|>> :representation))
+
   (def: dummy-checksum
     Checksum
     (:abstraction "        "))
@@ -116,8 +168,15 @@
     (format ..blank ..null))
 
   (def: checksum
+    (-> Binary Nat)
+    (binary.fold n.+ 0))
+
+  (def: checksum-checksum
+    (|> ..dummy-checksum :representation encoding.to-utf8 ..checksum))
+
+  (def: checksum-code
     (-> Binary Checksum)
-    (|>> (binary.fold n.+ 0)
+    (|>> ..checksum
          ..coerce-small
          ..from-small
          (:: n.octal encode)
@@ -132,6 +191,18 @@
       (|>> :representation
            encoding.to-utf8
            (format.segment padded-size))))
+
+  (def: checksum-parser
+    (Parser [Nat Checksum])
+    (do <>.monad
+      [ascii (<b>.segment ..small-size)
+       digits (<>.lift
+               (encoding.from-utf8 ascii))
+       _ ..verify-small-suffix
+       value (<>.lift
+              (:: n.octal decode digits))]
+      (wrap [value
+             (:abstraction (format digits ..checksum-suffix))])))
   )
 
 (def: last-ascii
@@ -150,11 +221,27 @@
   (exception.report
    ["Text" (%.text text)]))
 
-(def: name-size Size 31)
-(def: path-size Size 99)
-
-(template [<type> <representation> <size> <exception> <in> <out> <writer> <none>]
-  [(abstract: <type>
+(def: #export name-size Size 31)
+(def: #export path-size Size 99)
+
+(def: (un-pad string)
+  (-> Binary (Try Binary))
+  (case (binary.size string)
+    0 (#try.Success string)
+    size (loop [end (dec size)]
+           (case end
+             0 (#try.Success (encoding.to-utf8 ""))
+             _ (do try.monad
+                 [last-char (binary.read/8 end string)]
+                 (`` (case (.nat last-char)
+                       (^ (char (~~ (static ..null))))
+                       (recur (dec end))
+
+                       _
+                       (binary.slice 0 end string))))))))
+
+(template [<type> <representation> <size> <exception> <in> <out> <writer> <parser> <none>]
+  [(abstract: #export <type>
      {}
 
      <representation>
@@ -168,12 +255,12 @@
      (def: #export (<in> value)
        (-> <representation> (Try <type>))
        (if (..ascii? value)
-         (if (|> value encoding.to-utf8 binary.size (n.< <size>))
+         (if (|> value encoding.to-utf8 binary.size (n.<= <size>))
            (#try.Success (:abstraction value))
            (exception.throw <exception> [value]))
          (exception.throw ..not-ascii [value])))
 
-     (def: <out>
+     (def: #export <out>
        (-> <type> <representation>)
        (|>> :representation))
 
@@ -186,13 +273,27 @@
               encoding.to-utf8
               (format.segment padded-size))))
 
+     (def: <parser>
+       (Parser <type>)
+       (do <>.monad
+         [string (<b>.segment <size>)
+          end <b>.bits/8
+          #let [expected (`` (char (~~ (static ..null))))]
+          _ (<>.assert (exception.construct ..wrong-character [expected end])
+                       (n.= expected end))]
+         (<>.lift
+          (do {@ try.monad}
+            [ascii (..un-pad string)
+             text (encoding.from-utf8 ascii)]
+            (<in> text)))))
+
      (def: #export <none>
        <type>
        (try.assume (<in> "")))
      )]
 
-  [Name Text      ..name-size name-is-too-long name from-name name-writer anonymous]
-  [Path file.Path ..path-size path-is-too-long path from-path path-writer no-path]
+  [Name Text      ..name-size name-is-too-long name from-name name-writer name-parser anonymous]
+  [Path file.Path ..path-size path-is-too-long path from-path path-writer path-parser no-path]
   )
 
 (def: magic-size Size 7)
@@ -215,6 +316,18 @@
       (|>> :representation
            encoding.to-utf8
            (format.segment padded-size))))
+
+  (def: magic-parser
+    (Parser Magic)
+    (do <>.monad
+      [string (<b>.segment ..magic-size)
+       end <b>.bits/8
+       #let [expected (`` (char (~~ (static ..null))))]
+       _ (<>.assert (exception.construct ..wrong-character [expected end])
+                    (n.= expected end))]
+      (<>.lift
+       (:: try.monad map (|>> :abstraction)
+           (encoding.from-utf8 string)))))
   )
 
 (def: block-size Size 512)
@@ -278,29 +391,49 @@
 
   Char
 
-  (def: old-normal
-    Link-Flag
-    (:abstraction 0))
-
-  (template [<flag> <name>]
-    [(def: <name>
-       Link-Flag
-       (:abstraction (char <flag>)))]
-
-    ["0" normal]
-    ["1" link]
-    ["2" symbolic-link]
-    ["3" character]
-    ["4" block]
-    ["5" directory]
-    ["6" fifo]
-    ["7" contiguous]
-    )
+  (def: link-flag
+    (-> Link-Flag Char)
+    (|>> :representation))
 
   (def: link-flag-writer
     (Writer Link-Flag)
     (|>> :representation
          format.bits/8))
+
+  (with-expansions [<options> (as-is [0 old-normal]
+                                     [(char "0") normal]
+                                     [(char "1") link]
+                                     [(char "2") symbolic-link]
+                                     [(char "3") character]
+                                     [(char "4") block]
+                                     [(char "5") directory]
+                                     [(char "6") fifo]
+                                     [(char "7") contiguous])]
+    (template [<flag> <name>]
+      [(def: <name>
+         Link-Flag
+         (:abstraction <flag>))]
+
+      <options>
+      )
+
+    (exception: #export (invalid-link-flag {value Nat})
+      (exception.report
+       ["Value" (%.nat value)]))
+
+    (def: link-flag-parser
+      (Parser Link-Flag)
+      (do <>.monad
+        [linkflag <b>.bits/8]
+        (case (.nat linkflag)
+          (^template [<value> <link-flag>]
+            (^ <value>)
+            (wrap <link-flag>))
+          (<options>)
+
+          _
+          (<>.lift
+           (exception.throw ..invalid-link-flag [(.nat linkflag)]))))))
   )
 
 (abstract: #export Mode
@@ -308,27 +441,9 @@
 
   Nat
 
-  (template [<code> <name>]
-    [(def: #export <name>
-       Mode
-       (:abstraction (number.oct <code>)))]
-
-    ["0001" execute-by-other]
-    ["0002" write-by-other]
-    ["0004" read-by-other]
-
-    ["0010" execute-by-group]
-    ["0020" write-by-group]
-    ["0040" read-by-group]
-
-    ["0100" execute-by-owner]
-    ["0200" write-by-owner]
-    ["0400" read-by-owner]
-
-    ["1000" save-text]
-    ["2000" set-group-id-on-execution]
-    ["4000" set-user-id-on-execution]
-    )
+  (def: #export mode
+    (-> Mode Nat)
+    (|>> :representation))
 
   (def: #export (and left right)
     (-> Mode Mode Mode)
@@ -342,6 +457,67 @@
          ..small
          try.assume
          ..small-writer))
+
+  (exception: #export (invalid-mode {value Nat})
+    (exception.report
+     ["Value" (%.nat value)]))
+
+  (with-expansions [<options> (as-is ["0000" none]
+                                     
+                                     ["0001" execute-by-other]
+                                     ["0002" write-by-other]
+                                     ["0004" read-by-other]
+
+                                     ["0010" execute-by-group]
+                                     ["0020" write-by-group]
+                                     ["0040" read-by-group]
+
+                                     ["0100" execute-by-owner]
+                                     ["0200" write-by-owner]
+                                     ["0400" read-by-owner]
+
+                                     ["1000" save-text]
+                                     ["2000" set-group-id-on-execution]
+                                     ["4000" set-user-id-on-execution])]
+    (template [<code> <name>]
+      [(def: #export <name>
+         Mode
+         (:abstraction (number.oct <code>)))]
+
+      <options>
+      )
+
+    (def: maximum-mode
+      Mode
+      ($_ and
+          ..none
+          
+          ..execute-by-other
+          ..write-by-other
+          ..read-by-other
+
+          ..execute-by-group
+          ..write-by-group
+          ..read-by-group
+
+          ..execute-by-owner
+          ..write-by-owner
+          ..read-by-owner
+
+          ..save-text
+          ..set-group-id-on-execution
+          ..set-user-id-on-execution
+          ))
+
+    (def: mode-parser
+      (Parser Mode)
+      (do {@ <>.monad}
+        [value (:: @ map ..from-small ..small-parser)]
+        (if (n.<= (:representation ..maximum-mode)
+                  value)
+          (wrap (:abstraction value))
+          (<>.lift
+           (exception.throw ..invalid-mode [value]))))))
   )
 
 (def: maximum-content-size
@@ -350,7 +526,7 @@
       (list.repeat ..content-size)
       (list@fold n.* 1)))
 
-(abstract: Content
+(abstract: #export Content
   {}
 
   [Big Binary]
@@ -364,6 +540,10 @@
   (def: from-content
     (-> Content [Big Binary])
     (|>> :representation))
+
+  (def: #export data
+    (-> Content Binary)
+    (|>> :representation product.right))
   )
 
 (type: #export ID
@@ -384,14 +564,16 @@
 (type: #export File
   [Path Instant Mode Ownership Content])
 
-(type: #export Directory
-  Path)
+(type: #export Normal File)
+(type: #export Symbolic-Link Path)
+(type: #export Directory Path)
+(type: #export Contiguous File)
 
 (type: #export Entry
-  (#Normal File)
-  (#Symbolic-Link Path)
-  (#Directory Directory)
-  (#Contiguous File))
+  (#Normal ..Normal)
+  (#Symbolic-Link ..Symbolic-Link)
+  (#Directory ..Directory)
+  (#Contiguous ..Contiguous))
 
 (type: #export Device
   Small)
@@ -456,11 +638,10 @@
   (let [checksum (|> header
                      (set@ #checksum ..dummy-checksum)
                      (format.run ..header-writer')
-                     ..checksum)
-        data (|> header
-                 (set@ #checksum checksum)
-                 (format.run ..header-writer'))]
-    (|> data
+                     ..checksum-code)]
+    (|> header
+        (set@ #checksum checksum)
+        (format.run ..header-writer')
         (format.segment ..block-size))))
 
 (def: modification-time
@@ -523,7 +704,7 @@
     #minor-device ..no-device}))
 
 (def: (directory-writer path)
-  (Writer Directory)
+  (Writer Path)
   (..header-writer
    {#path path
     #mode ($_ ..and
@@ -563,3 +744,144 @@
                             format@identity
                             tar)
                   (format.segment ..end-of-archive-size ..end-of-archive)))
+
+(exception: #export (wrong-checksum {expected Nat} {actual Nat})
+  (exception.report
+   ["Expected" (%.nat expected)]
+   ["Actual" (%.nat actual)]))
+
+(def: header-padding-size
+  (n.- header-size block-size))
+
+## When the checksum gets originally calculated, the assumption is that all the characters in the checksum field
+## of the header will be spaces.
+## This means that just calculating the checksum of the 512 bytes of the header, when reading them, would yield
+## an incorrect result, as the contents of the checksum field would be an actual checksum, instead of just spaces.
+## To correct for this, it is necessary to calculate the checksum of just the checksum field, subtract that, and then
+## add-in the checksum of the spaces.
+(def: (expected-checksum checksum header)
+  (-> Checksum Binary Nat)
+  (let [|checksum| (|> checksum ..from-checksum encoding.to-utf8 ..checksum)]
+    (|> (..checksum header)
+        (n.- |checksum|)
+        (n.+ ..checksum-checksum))))
+
+(def: header-parser
+  (Parser Header)
+  (do <>.monad
+    [binary-header (<>.speculative (<b>.segment block-size))
+     path ..path-parser
+     mode ..mode-parser
+     user-id ..small-parser
+     group-id ..small-parser
+     size ..big-parser
+     modification-time ..big-parser
+     [actual checksum-code] ..checksum-parser
+     _ (let [expected (expected-checksum checksum-code binary-header)]
+         (<>.lift
+          (exception.assert ..wrong-checksum [expected actual]
+                            (n.= expected actual))))
+     link-flag ..link-flag-parser
+     link-name ..path-parser
+     magic ..magic-parser
+     user-name ..name-parser
+     group-name ..name-parser
+     major-device ..small-parser
+     minor-device ..small-parser
+     _ (<b>.segment ..header-padding-size)]
+    (wrap {#path path
+           #mode mode
+           #user-id user-id
+           #group-id group-id
+           #size size
+           #modification-time modification-time
+           #checksum checksum-code
+           #link-flag link-flag
+           #link-name link-name
+           #magic magic
+           #user-name user-name
+           #group-name group-name
+           #major-device major-device
+           #minor-device minor-device})))
+
+(exception: #export (wrong-link-flag {expected Link-Flag} {actual Link-Flag})
+  (exception.report
+   ["Expected" (%.nat (..link-flag expected))]
+   ["Actual" (%.nat (..link-flag actual))]))
+
+(def: (file-parser expected)
+  (-> Link-Flag (Parser File))
+  (do <>.monad
+    [header ..header-parser
+     _ (<>.assert (exception.construct ..wrong-link-flag [expected (get@ #link-flag header)])
+                  (is? expected (get@ #link-flag header)))
+     #let [size (get@ #size header)
+           rounded-size (..rounded-content-size size)]
+     content (<b>.segment (..from-big size))
+     content (<>.lift (..content content))
+     _ (<b>.segment (n.- (..from-big size) rounded-size))]
+    (wrap [(get@ #path header)
+           (|> header
+               (get@ #modification-time)
+               ..from-big
+               .int
+               duration.from-millis
+               (duration.scale-up (|> duration.second duration.to-millis .nat))
+               instant.absolute)
+           (get@ #mode header)
+           {#user {#name (get@ #user-name header)
+                   #id (get@ #user-id header)}
+            #group {#name (get@ #group-name header)
+                    #id (get@ #group-id header)}}
+           content])))
+
+(def: (file-name-parser expected extractor)
+  (-> Link-Flag (-> Header Path) (Parser Path))
+  (do <>.monad
+    [header ..header-parser
+     _ (<>.lift
+        (exception.assert ..wrong-link-flag [expected (get@ #link-flag header)]
+                          (n.= (..link-flag expected)
+                               (..link-flag (get@ #link-flag header)))))]
+    (wrap (extractor header))))
+
+(def: entry-parser
+  (Parser Entry)
+  ($_ <>.either
+      (:: <>.monad map (|>> #..Normal)
+          (<>.either (..file-parser ..normal)
+                     (..file-parser ..old-normal)))
+      (:: <>.monad map (|>> #..Symbolic-Link)
+          (..file-name-parser ..symbolic-link (get@ #link-name)))
+      (:: <>.monad map (|>> #..Directory)
+          (..file-name-parser ..directory (get@ #path)))
+      (:: <>.monad map (|>> #..Contiguous)
+          (..file-parser ..contiguous))))
+
+## It's safe to implement the parser this way because the range of values for Nat is 2^64
+## Whereas the maximum possible value for the checksum of a 512 block is (256 × 512) = 131,072
+(def: end-of-archive-block-parser
+  (Parser Any)
+  (do <>.monad
+    [block (<b>.segment ..block-size)]
+    (let [actual (..checksum block)]
+      (<>.lift
+       (exception.assert ..wrong-checksum [0 actual]
+                         (n.= 0 actual))))))
+
+(exception: #export invalid-end-of-archive)
+
+(def: end-of-archive-parser
+  (Parser Any)
+  (do <>.monad
+    [_ (<>.at-most 2 end-of-archive-block-parser)
+     done? <b>.end?]
+    (<>.lift
+     (exception.assert ..invalid-end-of-archive []
+                       done?))))
+
+(def: #export parser
+  (Parser Tar)
+  (|> (<>.some entry-parser)
+      (:: <>.monad map row.from-list)
+      (<>.before ..end-of-archive-parser)))
diff --git a/stdlib/source/lux/time/duration.lux b/stdlib/source/lux/time/duration.lux
index 47a480ab9..b87c2e2d3 100644
--- a/stdlib/source/lux/time/duration.lux
+++ b/stdlib/source/lux/time/duration.lux
@@ -60,11 +60,15 @@
     (-> Duration Duration Int)
     (i./ (:representation param) (:representation subject)))
 
-  (structure: #export equivalence (Equivalence Duration)
+  (structure: #export equivalence
+    (Equivalence Duration)
+    
     (def: (= param subject)
       (i.= (:representation param) (:representation subject))))
 
-  (structure: #export order (Order Duration)
+  (structure: #export order
+    (Order Duration)
+    
     (def: &equivalence ..equivalence)
     (def: (< param subject)
       (i.< (:representation param) (:representation subject))))
@@ -96,7 +100,9 @@
 
 (def: #export leap-year (merge day normal-year))
 
-(structure: #export monoid (Monoid Duration)
+(structure: #export monoid
+  (Monoid Duration)
+  
   (def: identity ..empty)
   (def: compose ..merge))
 
diff --git a/stdlib/source/lux/time/instant.lux b/stdlib/source/lux/time/instant.lux
index bd378016a..ab7fe6953 100644
--- a/stdlib/source/lux/time/instant.lux
+++ b/stdlib/source/lux/time/instant.lux
@@ -14,7 +14,7 @@
    [data
     ["." maybe]
     [number
-     ["n" nat]
+     ["n" nat ("#@." decimal)]
      ["i" int ("#@." decimal)]]
     ["." text ("#@." monoid)]
     [collection
@@ -56,16 +56,22 @@
     (-> Duration Instant)
     (|> offset duration.to-millis :abstraction))
 
-  (structure: #export equivalence (Equivalence Instant)
+  (structure: #export equivalence
+    (Equivalence Instant)
+    
     (def: (= param subject)
       (:: i.equivalence = (:representation param) (:representation subject))))
 
-  (structure: #export order (Order Instant)
+  (structure: #export order
+    (Order Instant)
+    
     (def: &equivalence ..equivalence)
     (def: (< param subject)
       (:: i.order < (:representation param) (:representation subject))))
 
-  (`` (structure: #export enum (Enum Instant)
+  (`` (structure: #export enum
+        (Enum Instant)
+        
         (def: &order ..order)
         (~~ (template [<name>]
               [(def: <name>
@@ -126,10 +132,10 @@
               (row.reverse months))))
 
 (def: (pad value)
-  (-> Int Text)
-  (if (i.< +10 value)
-    (text@compose "0" (i@encode value))
-    (i@encode value)))
+  (-> Nat Text)
+  (if (n.< 10 value)
+    (text@compose "0" (n@encode value))
+    (n@encode value)))
 
 (def: (adjust-negative space duration)
   (-> Duration Duration Duration)
@@ -138,12 +144,12 @@
     duration))
 
 (def: (encode-millis millis)
-  (-> Int Text)
-  (cond (i.= +0 millis)   ""
-        (i.< +10 millis)  ($_ text@compose ".00" (i@encode millis))
-        (i.< +100 millis) ($_ text@compose ".0" (i@encode millis))
-        ## (i.< +1,000 millis)
-        ($_ text@compose "." (i@encode millis))))
+  (-> Nat Text)
+  (cond (n.= 0 millis)   ""
+        (n.< 10 millis)  ($_ text@compose ".00" (n@encode millis))
+        (n.< 100 millis) ($_ text@compose ".0" (n@encode millis))
+        ## (n.< 1,000 millis)
+        ($_ text@compose "." (n@encode millis))))
 
 (def: seconds-per-day Int (duration.query duration.second duration.day))
 (def: days-up-to-epoch Int +719468)
@@ -196,11 +202,12 @@
         [hours day-time] [(duration.query duration.hour day-time) (duration.frame duration.hour day-time)]
         [minutes day-time] [(duration.query duration.minute day-time) (duration.frame duration.minute day-time)]
         [seconds millis] [(duration.query duration.second day-time) (duration.frame duration.second day-time)]]
-    ($_ text@compose (i@encode year) "-" (pad month) "-" (pad day) "T"
-        (pad hours) ":" (pad minutes) ":" (pad seconds)
+    ($_ text@compose (i@encode year) "-" (pad (.nat month)) "-" (pad (.nat day)) "T"
+        (pad (.nat hours)) ":" (pad (.nat minutes)) ":" (pad (.nat seconds))
         (|> millis
             (adjust-negative duration.second)
             duration.to-millis
+            .nat
             encode-millis)
         "Z")))
 
diff --git a/stdlib/source/spec/lux/abstract/functor/contravariant.lux b/stdlib/source/spec/lux/abstract/functor/contravariant.lux
new file mode 100644
index 000000000..b21e28e68
--- /dev/null
+++ b/stdlib/source/spec/lux/abstract/functor/contravariant.lux
@@ -0,0 +1,31 @@
+(.module:
+  [lux #*
+   [abstract
+    [equivalence (#+ Equivalence)]
+    [monad (#+ do)]]
+   [data
+    [number
+     ["n" nat]]]
+   [control
+    ["." function]]
+   [math
+    ["." random]]
+   ["_" test (#+ Test)]]
+  {1
+   ["." / (#+ Functor)]})
+
+(def: (identity equivalence value (^open "/@."))
+  (All [f a] (-> (Equivalence (f a)) (f a) (Functor f) Test))
+  (_.test "Law of identity."
+          (equivalence
+           (/@map function.identity value)
+           value)))
+
+(def: #export (spec equivalence value functor)
+  (All [f a] (-> (Equivalence (f a)) (f a) (Functor f) Test))
+  (do random.monad
+    [sample random.nat]
+    (<| (_.with-cover [/.Functor])
+        ($_ _.and
+            (..identity equivalence value functor)
+            ))))
diff --git a/stdlib/source/test/lux/abstract.lux b/stdlib/source/test/lux/abstract.lux
index ef7cb0774..aa93df86f 100644
--- a/stdlib/source/test/lux/abstract.lux
+++ b/stdlib/source/test/lux/abstract.lux
@@ -14,7 +14,16 @@
    ["#." monad]
    ["#." monoid]
    ["#." order]
-   ["#." predicate]])
+   ["#." predicate]
+   [functor
+    ["#." contravariant]]])
+
+(def: functor
+  Test
+  ($_ _.and
+      /functor.test
+      /contravariant.test
+      ))
 
 (def: #export test
   Test
@@ -25,7 +34,7 @@
       /enum.test
       /equivalence.test
       /fold.test
-      /functor.test
+      ..functor
       /hash.test
       /interval.test
       /monad.test
diff --git a/stdlib/source/test/lux/abstract/equivalence.lux b/stdlib/source/test/lux/abstract/equivalence.lux
index 7cc5c95f9..d79803e31 100644
--- a/stdlib/source/test/lux/abstract/equivalence.lux
+++ b/stdlib/source/test/lux/abstract/equivalence.lux
@@ -1,7 +1,12 @@
 (.module:
   [lux #*
    ["_" test (#+ Test)]
-   [abstract/monad (#+ do)]
+   [abstract
+    [monad (#+ do)]
+    {[0 #spec]
+     [/
+      [functor
+       ["." contravariant]]]}]
    [data
     ["." bit ("#@." equivalence)]
     [number
@@ -20,9 +25,20 @@
      leftI random.int
      rightI random.int
      sample random.nat
-     different (|> random.nat (random.filter (|>> (n.= sample) not)))]
+     different (|> random.nat (random.filter (|>> (n.= sample) not)))
+     #let [equivalence (: (Equivalence (Equivalence Nat))
+                          (structure
+                           (def: (= left right)
+                             (and (bit@= (:: left = leftN leftN)
+                                         (:: right = leftN leftN))
+                                  (bit@= (:: left = rightN rightN)
+                                         (:: right = rightN rightN))
+                                  (bit@= (:: left = leftN rightN)
+                                         (:: right = leftN rightN))))))]]
     (<| (_.covering /._)
         ($_ _.and
+            (_.with-cover [/.functor]
+              (contravariant.spec equivalence n.equivalence /.functor))
             (_.cover [/.sum]
                      (let [equivalence (/.sum n.equivalence i.equivalence)]
                        (and (bit@= (:: n.equivalence = leftN leftN)
diff --git a/stdlib/source/test/lux/abstract/functor/contravariant.lux b/stdlib/source/test/lux/abstract/functor/contravariant.lux
new file mode 100644
index 000000000..93d1f18ad
--- /dev/null
+++ b/stdlib/source/test/lux/abstract/functor/contravariant.lux
@@ -0,0 +1,10 @@
+(.module:
+  [lux #*
+   ["_" test (#+ Test)]]
+  {1
+   ["." /]})
+
+(def: #export test
+  Test
+  (<| (_.covering /._)
+      (_.in-parallel (list))))
diff --git a/stdlib/source/test/lux/abstract/order.lux b/stdlib/source/test/lux/abstract/order.lux
index 7157a6c01..dff849034 100644
--- a/stdlib/source/test/lux/abstract/order.lux
+++ b/stdlib/source/test/lux/abstract/order.lux
@@ -2,7 +2,11 @@
   [lux #*
    ["_" test (#+ Test)]
    [abstract
-    [monad (#+ do)]]
+    [monad (#+ do)]
+    {[0 #spec]
+     [/
+      [functor
+       ["." contravariant]]]}]
    [data
     ["." bit ("#@." equivalence)]
     [number
@@ -10,15 +14,28 @@
    [math
     ["." random (#+ Random)]]]
   {1
-   ["." / (#+ Order)]})
+   ["." / (#+ Order)
+    [//
+     [equivalence (#+ Equivalence)]]]})
 
 (def: #export test
   Test
   (<| (_.covering /._)
       (do random.monad
         [left random.nat
-         right (|> random.nat (random.filter (|>> (n.= left) not)))])
+         right (|> random.nat (random.filter (|>> (n.= left) not)))
+         #let [equivalence (: (Equivalence (Order Nat))
+                              (structure
+                               (def: (= leftO rightO)
+                                 (and (bit@= (:: leftO < left left)
+                                             (:: rightO < left left))
+                                      (bit@= (:: leftO < right right)
+                                             (:: rightO < right right))
+                                      (bit@= (:: leftO < left right)
+                                             (:: rightO < left right))))))]])
       ($_ _.and
+          (_.with-cover [/.functor]
+            (contravariant.spec equivalence n.order /.functor))
           (_.cover [/.Choice /.min /.max]
                    (n.< (/.max n.order left right)
                         (/.min n.order left right)))
diff --git a/stdlib/source/test/lux/data.lux b/stdlib/source/test/lux/data.lux
index fa544ccd5..47a79b530 100644
--- a/stdlib/source/test/lux/data.lux
+++ b/stdlib/source/test/lux/data.lux
@@ -30,6 +30,7 @@
     ["#/." regex]]
    [format
     ["#." json]
+    ["#." tar]
     ["#." xml]]
    ["#." collection]])
 
@@ -71,6 +72,7 @@
 (def: format
   ($_ _.and
       /json.test
+      /tar.test
       /xml.test
       ))
 
diff --git a/stdlib/source/test/lux/data/format/tar.lux b/stdlib/source/test/lux/data/format/tar.lux
new file mode 100644
index 000000000..b8ba1af51
--- /dev/null
+++ b/stdlib/source/test/lux/data/format/tar.lux
@@ -0,0 +1,409 @@
+(.module:
+  [lux #*
+   ["_" test (#+ Test)]
+   [abstract
+    [monad (#+ do)]]
+   [control
+    ["." try]
+    ["." exception]
+    ["<>" parser
+     ["<b>" binary]]]
+   [data
+    ["." product]
+    ["." maybe]
+    ["." binary ("#@." equivalence)]
+    ["." text ("#@." equivalence)
+     ["." encoding]
+     ["." unicode]
+     ["%" format (#+ format)]]
+    [number
+     ["n" nat]
+     ["i" int]]
+    [collection
+     ["." row]
+     ["." list ("#@." fold)]]
+    ["." format #_
+     ["#" binary]]]
+   [time
+    ["." instant (#+ Instant)]
+    ["." duration]]
+   [math
+    ["." random (#+ Random)]]]
+  {1
+   ["." /]})
+
+(def: path
+  Test
+  (_.with-cover [/.Path]
+    (do {@ random.monad}
+      [expected (random.ascii/lower-alpha /.path-size)
+       invalid (random.ascii/lower-alpha (inc /.path-size))
+       not-ascii (random.text (random.char (unicode.set (list unicode.katakana)))
+                              /.path-size)]
+      (`` ($_ _.and
+              (_.cover [/.path /.from-path]
+                       (case (/.path expected)
+                         (#try.Success actual)
+                         (text@= expected
+                                 (/.from-path actual))
+
+                         (#try.Failure error)
+                         false))
+              (_.cover [/.path-size /.path-is-too-long]
+                       (case (/.path invalid)
+                         (#try.Success _)
+                         false
+
+                         (#try.Failure error)
+                         (exception.match? /.path-is-too-long error)))
+              (_.cover [/.not-ascii]
+                       (case (/.path not-ascii)
+                         (#try.Success actual)
+                         false
+
+                         (#try.Failure error)
+                         (exception.match? /.not-ascii error)))
+              )))))
+
+(def: name
+  Test
+  (_.with-cover [/.Name]
+    (do {@ random.monad}
+      [expected (random.ascii/lower-alpha /.name-size)
+       invalid (random.ascii/lower-alpha (inc /.name-size))
+       not-ascii (random.text (random.char (unicode.set (list unicode.katakana)))
+                              /.name-size)]
+      (`` ($_ _.and
+              (_.cover [/.name /.from-name]
+                       (case (/.name expected)
+                         (#try.Success actual)
+                         (text@= expected
+                                 (/.from-name actual))
+
+                         (#try.Failure error)
+                         false))
+              (_.cover [/.name-size /.name-is-too-long]
+                       (case (/.name invalid)
+                         (#try.Success _)
+                         false
+
+                         (#try.Failure error)
+                         (exception.match? /.name-is-too-long error)))
+              (_.cover [/.not-ascii]
+                       (case (/.name not-ascii)
+                         (#try.Success actual)
+                         false
+
+                         (#try.Failure error)
+                         (exception.match? /.not-ascii error)))
+              )))))
+
+(def: small
+  Test
+  (_.with-cover [/.Small]
+    (do {@ random.monad}
+      [expected (|> random.nat (:: @ map (n.% /.small-limit)))
+       invalid (|> random.nat (:: @ map (n.max /.small-limit)))]
+      (`` ($_ _.and
+              (_.cover [/.small /.from-small]
+                       (case (/.small expected)
+                         (#try.Success actual)
+                         (n.= expected
+                              (/.from-small actual))
+
+                         (#try.Failure error)
+                         false))
+              (_.cover [/.small-limit /.not-a-small-number]
+                       (case (/.small invalid)
+                         (#try.Success actual)
+                         false
+
+                         (#try.Failure error)
+                         (exception.match? /.not-a-small-number error)))
+              )))))
+
+(def: big
+  Test
+  (_.with-cover [/.Big]
+    (do {@ random.monad}
+      [expected (|> random.nat (:: @ map (n.% /.big-limit)))
+       invalid (|> random.nat (:: @ map (n.max /.big-limit)))]
+      (`` ($_ _.and
+              (_.cover [/.big /.from-big]
+                       (case (/.big expected)
+                         (#try.Success actual)
+                         (n.= expected
+                              (/.from-big actual))
+
+                         (#try.Failure error)
+                         false))
+              (_.cover [/.big-limit /.not-a-big-number]
+                       (case (/.big invalid)
+                         (#try.Success actual)
+                         false
+
+                         (#try.Failure error)
+                         (exception.match? /.not-a-big-number error)))
+              )))))
+
+(def: chunk-size 32)
+
+(def: entry
+  Test
+  (do {@ random.monad}
+    [expected-path (random.ascii/lower-alpha (dec /.path-size))
+     expected-moment (:: @ map (|>> (n.% 1,00,00,00,00,00,000) .int instant.from-millis)
+                         random.nat)
+     chunk (random.ascii/lower-alpha chunk-size)
+     chunks (:: @ map (n.% 100) random.nat)
+     #let [content (|> chunk
+                       (list.repeat chunks)
+                       (text.join-with "")
+                       encoding.to-utf8)]]
+    (`` ($_ _.and
+            (~~ (template [<type> <tag>]
+                  [(_.cover [<type>]
+                            (|> (do try.monad
+                                  [expected-path (/.path expected-path)
+                                   tar (|> (row.row (<tag> expected-path))
+                                           (format.run /.writer)
+                                           (<b>.run /.parser))]
+                                  (wrap (case (row.to-list tar)
+                                          (^ (list (<tag> actual-path)))
+                                          (text@= (/.from-path expected-path)
+                                                  (/.from-path actual-path))
+
+                                          _
+                                          false)))
+                                (try.default false)))]
+
+                  [/.Symbolic-Link #/.Symbolic-Link]
+                  [/.Directory #/.Directory]
+                  ))
+            (_.with-cover [/.File /.Content /.content /.data]
+              ($_ _.and
+                  (~~ (template [<type> <tag>]
+                        [(_.cover [<type>]
+                                  (|> (do try.monad
+                                        [expected-path (/.path expected-path)
+                                         expected-content (/.content content)
+                                         tar (|> (row.row (<tag> [expected-path
+                                                                  expected-moment
+                                                                  /.none
+                                                                  {#/.user {#/.name /.anonymous
+                                                                            #/.id /.no-id}
+                                                                   #/.group {#/.name /.anonymous
+                                                                             #/.id /.no-id}}
+                                                                  expected-content]))
+                                                 (format.run /.writer)
+                                                 (<b>.run /.parser))]
+                                        (wrap (case (row.to-list tar)
+                                                (^ (list (<tag> [actual-path actual-moment actual-mode actual-ownership actual-content])))
+                                                (let [seconds (: (-> Instant Int)
+                                                                 (|>> instant.relative (duration.query duration.second)))]
+                                                  (and (text@= (/.from-path expected-path)
+                                                               (/.from-path actual-path))
+                                                       (i.= (seconds expected-moment)
+                                                            (seconds actual-moment))
+                                                       (binary@= (/.data expected-content)
+                                                                 (/.data actual-content))))
+
+                                                _
+                                                false)))
+                                      (try.default false)))]
+
+                        [/.Normal #/.Normal]
+                        [/.Contiguous #/.Contiguous]
+                        ))))))))
+
+(def: random-mode
+  (Random /.Mode)
+  (do {@ random.monad}
+    []
+    (random.either (random.either (random.either (wrap /.execute-by-other)
+                                                 (wrap /.write-by-other))
+                                  (random.either (wrap /.read-by-other)
+                                                 (wrap /.execute-by-group)))
+                   (random.either (random.either (random.either (wrap /.write-by-group)
+                                                                (wrap /.read-by-group))
+                                                 (random.either (wrap /.execute-by-owner)
+                                                                (wrap /.write-by-owner)))
+                                  (random.either (random.either (wrap /.read-by-owner)
+                                                                (wrap /.save-text))
+                                                 (random.either (wrap /.set-group-id-on-execution)
+                                                                (wrap /.set-user-id-on-execution)))))))
+
+(def: mode
+  Test
+  (_.with-cover [/.Mode /.mode]
+    (do {@ random.monad}
+      [path (random.ascii/lower-alpha 10)
+       modes (random.list 4 ..random-mode)
+       #let [expected-mode (list@fold /.and /.none modes)]]
+      (`` ($_ _.and
+              (_.cover [/.and]
+                       (|> (do try.monad
+                             [path (/.path path)
+                              content (/.content (binary.create 0))
+                              tar (|> (row.row (#/.Normal [path
+                                                           (instant.from-millis +0)
+                                                           expected-mode
+                                                           {#/.user {#/.name /.anonymous
+                                                                     #/.id /.no-id}
+                                                            #/.group {#/.name /.anonymous
+                                                                      #/.id /.no-id}}
+                                                           content]))
+                                      (format.run /.writer)
+                                      (<b>.run /.parser))]
+                             (wrap (case (row.to-list tar)
+                                     (^ (list (#/.Normal [_ _ actual-mode _ _])))
+                                     (n.= (/.mode expected-mode)
+                                          (/.mode actual-mode))
+
+                                     _
+                                     false)))
+                           (try.default false)))
+              (~~ (template [<expected-mode>]
+                    [(_.cover [<expected-mode>]
+                              (|> (do try.monad
+                                    [path (/.path path)
+                                     content (/.content (binary.create 0))
+                                     tar (|> (row.row (#/.Normal [path
+                                                                  (instant.from-millis +0)
+                                                                  <expected-mode>
+                                                                  {#/.user {#/.name /.anonymous
+                                                                            #/.id /.no-id}
+                                                                   #/.group {#/.name /.anonymous
+                                                                             #/.id /.no-id}}
+                                                                  content]))
+                                             (format.run /.writer)
+                                             (<b>.run /.parser))]
+                                    (wrap (case (row.to-list tar)
+                                            (^ (list (#/.Normal [_ _ actual-mode _ _])))
+                                            (n.= (/.mode <expected-mode>)
+                                                 (/.mode actual-mode))
+
+                                            _
+                                            false)))
+                                  (try.default false)))]
+
+                    [/.none]
+
+                    [/.execute-by-other]
+                    [/.write-by-other]
+                    [/.read-by-other]
+
+                    [/.execute-by-group]
+                    [/.write-by-group]
+                    [/.read-by-group]
+
+                    [/.execute-by-owner]
+                    [/.write-by-owner]
+                    [/.read-by-owner]
+
+                    [/.save-text]
+                    [/.set-group-id-on-execution]
+                    [/.set-user-id-on-execution]
+                    )))))))
+
+(def: ownership
+  Test
+  (do {@ random.monad}
+    [path (random.ascii/lower-alpha /.path-size)
+     expected (random.ascii/lower-alpha /.name-size)
+     invalid (random.ascii/lower-alpha (inc /.name-size))
+     not-ascii (random.text (random.char (unicode.set (list unicode.katakana)))
+                            /.name-size)]
+    (_.with-cover [/.Ownership /.Owner /.ID]
+      ($_ _.and
+          (_.cover [/.name-size /.name-is-too-long]
+                   (case (/.name invalid)
+                     (#try.Success _)
+                     false
+
+                     (#try.Failure error)
+                     (exception.match? /.name-is-too-long error)))
+          (_.cover [/.not-ascii]
+                   (case (/.name not-ascii)
+                     (#try.Success actual)
+                     false
+
+                     (#try.Failure error)
+                     (exception.match? /.not-ascii error)))
+          (_.cover [/.Name /.name /.from-name]
+                   (|> (do try.monad
+                         [path (/.path path)
+                          content (/.content (binary.create 0))
+                          expected (/.name expected)
+                          tar (|> (row.row (#/.Normal [path
+                                                       (instant.from-millis +0)
+                                                       /.none
+                                                       {#/.user {#/.name expected
+                                                                 #/.id /.no-id}
+                                                        #/.group {#/.name /.anonymous
+                                                                  #/.id /.no-id}}
+                                                       content]))
+                                  (format.run /.writer)
+                                  (<b>.run /.parser))]
+                         (wrap (case (row.to-list tar)
+                                 (^ (list (#/.Normal [_ _ _ actual-ownership _])))
+                                 (and (text@= (/.from-name expected)
+                                              (/.from-name (get@ [#/.user #/.name] actual-ownership)))
+                                      (text@= (/.from-name /.anonymous)
+                                              (/.from-name (get@ [#/.group #/.name] actual-ownership))))
+                                 
+                                 _
+                                 false)))
+                       (try.default false)))
+          (_.cover [/.anonymous /.no-id]
+                   (|> (do try.monad
+                         [path (/.path path)
+                          content (/.content (binary.create 0))
+                          tar (|> (row.row (#/.Normal [path
+                                                       (instant.from-millis +0)
+                                                       /.none
+                                                       {#/.user {#/.name /.anonymous
+                                                                 #/.id /.no-id}
+                                                        #/.group {#/.name /.anonymous
+                                                                  #/.id /.no-id}}
+                                                       content]))
+                                  (format.run /.writer)
+                                  (<b>.run /.parser))]
+                         (wrap (case (row.to-list tar)
+                                 (^ (list (#/.Normal [_ _ _ actual-ownership _])))
+                                 (and (text@= (/.from-name /.anonymous)
+                                              (/.from-name (get@ [#/.user #/.name] actual-ownership)))
+                                      (n.= (/.from-small /.no-id)
+                                           (/.from-small (get@ [#/.user #/.id] actual-ownership)))
+                                      (text@= (/.from-name /.anonymous)
+                                              (/.from-name (get@ [#/.group #/.name] actual-ownership)))
+                                      (n.= (/.from-small /.no-id)
+                                           (/.from-small (get@ [#/.group #/.id] actual-ownership))))
+                                 
+                                 _
+                                 false)))
+                       (try.default false)))
+          ))))
+
+(def: #export test
+  Test
+  (<| (_.covering /._)
+      (_.with-cover [/.Tar]
+        ($_ _.and
+            (_.cover [/.writer /.parser]
+                     (|> row.empty
+                         (format.run /.writer)
+                         (<b>.run /.parser)
+                         (:: try.monad map row.empty?)
+                         (try.default false)))
+            ..path
+            ..name
+            ..small
+            ..big
+            (_.with-cover [/.Entry]
+              ($_ _.and
+                  ..entry
+                  ..mode
+                  ..ownership
+                  ))
+            ))))