From cf9e3fa6fef24cc0828ab882661fa96dc6f2570d Mon Sep 17 00:00:00 2001
From: Eduardo Julian
Date: Sun, 3 Feb 2019 11:53:21 -0400
Subject: Some refactoring around the identity function.

---
 stdlib/source/lux.lux                            |  9 ++--
 stdlib/source/lux/data/format/css/selector.lux   |  2 +-
 stdlib/source/lux/data/format/json.lux           | 17 +++----
 stdlib/source/lux/data/number.lux                | 64 +++++++++++-------------
 stdlib/source/lux/data/number/ratio.lux          |  7 +--
 stdlib/source/lux/function.lux                   | 25 +++++++--
 stdlib/source/lux/host.jvm.lux                   | 34 ++++++-------
 stdlib/source/lux/macro/syntax/common/writer.lux |  3 +-
 stdlib/test/test/lux.lux                         |  5 +-
 9 files changed, 85 insertions(+), 81 deletions(-)

diff --git a/stdlib/source/lux.lux b/stdlib/source/lux.lux
index d3a0f1825..b7de70c5d 100644
--- a/stdlib/source/lux.lux
+++ b/stdlib/source/lux.lux
@@ -3985,10 +3985,7 @@
       #None
       (fail "Wrong syntax for structure:"))))
 
-(def: #export (id x)
-  {#.doc "Identity function. Does nothing to it's argument and just returns it."}
-  (All [a] (-> a a))
-  x)
+(def: (identity x) (All [a] (-> a a)) x)
 
 (macro: #export (type: tokens)
   {#.doc (text$ ($_ "lux text concat"
@@ -5302,8 +5299,8 @@
              <open>
              parts-text
              <close>)]))
-    ([#Form   "(" ")" id]
-     [#Tuple  "[" "]" id]
+    ([#Form   "(" ")" ..identity]
+     [#Tuple  "[" "]" ..identity]
      [#Record "{" "}" rejoin-all-pairs])
 
     [new-cursor (#Rev value)]
diff --git a/stdlib/source/lux/data/format/css/selector.lux b/stdlib/source/lux/data/format/css/selector.lux
index 905012aeb..7b80e4973 100644
--- a/stdlib/source/lux/data/format/css/selector.lux
+++ b/stdlib/source/lux/data/format/css/selector.lux
@@ -1,5 +1,5 @@
 (.module:
-  [lux (#- or and for id is? not)
+  [lux (#- or and for is? not)
    [data
     ["." text
      format]]
diff --git a/stdlib/source/lux/data/format/json.lux b/stdlib/source/lux/data/format/json.lux
index 7d2e90270..edafe3178 100644
--- a/stdlib/source/lux/data/format/json.lux
+++ b/stdlib/source/lux/data/format/json.lux
@@ -296,7 +296,7 @@
   [string  Text #String  "string"]
   )
 
-(do-template [<test> <check> <type> <eq> <encoder> <tag> <desc> <pre>]
+(do-template [<test> <check> <type> <eq> <encoder> <tag> <desc>]
   [(def: #export (<test> test)
      {#.doc (code.text ($_ text/compose "Asks whether a JSON value is a " <desc> "."))}
      (-> <type> (Reader Bit))
@@ -304,7 +304,7 @@
        [head any]
        (case head
          (<tag> value)
-         (wrap (:: <eq> = test (<pre> value)))
+         (wrap (:: <eq> = test value))
 
          _
          (fail ($_ text/compose "JSON value is not " <desc> ".")))))
@@ -316,17 +316,16 @@
        [head any]
        (case head
          (<tag> value)
-         (let [value (<pre> value)]
-           (if (:: <eq> = test value)
-             (wrap [])
-             (fail ($_ text/compose "Value mismatch: " (<encoder> test) " =/= " (<encoder> value)))))
+         (if (:: <eq> = test value)
+           (wrap [])
+           (fail ($_ text/compose "Value mismatch: " (<encoder> test) " =/= " (<encoder> value))))
 
          _
          (fail ($_ text/compose "JSON value is not a " <desc> ".")))))]
 
-  [boolean? boolean! Bit  bit.Equivalence<Bit>     encode-boolean                      #Boolean "boolean" id]
-  [number?  number!  Frac number.Equivalence<Frac> (:: number.Codec<Text,Frac> encode) #Number  "number"  id]
-  [string?  string!  Text text.Equivalence<Text>   text.encode                         #String  "string"  id]
+  [boolean? boolean! Bit  bit.Equivalence<Bit>     encode-boolean                      #Boolean "boolean"]
+  [number?  number!  Frac number.Equivalence<Frac> (:: number.Codec<Text,Frac> encode) #Number  "number"]
+  [string?  string!  Text text.Equivalence<Text>   text.encode                         #String  "string"]
   )
 
 (def: #export (nullable parser)
diff --git a/stdlib/source/lux/data/number.lux b/stdlib/source/lux/data/number.lux
index e745d542a..f297f2788 100644
--- a/stdlib/source/lux/data/number.lux
+++ b/stdlib/source/lux/data/number.lux
@@ -12,14 +12,14 @@
    [data
     ["." error (#+ Error)]
     ["." maybe]
-    ["." text]
+    ["." text (#+ Char)]
     [collection
      ["." array (#+ Array)]]]
+   ["." function]
    ["." math]]
   [/
    ["." i64]])
 
-## [Structures]
 (do-template [<type> <test>]
   [(structure: #export _ (Equivalence <type>)
      (def: = <test>))]
@@ -44,14 +44,38 @@
   [Frac Equivalence<Frac> f/< f/<= f/> f/>=]
   )
 
+(do-template [<type> <order> <succ> <pred>]
+  [(structure: #export _ (Enum <type>)
+     (def: order <order>)
+     (def: succ <succ>)
+     (def: pred <pred>))]
+
+  [Nat  Order<Nat>  inc dec]
+  [Int  Order<Int>  inc dec]
+  [Frac Order<Frac> (f/+ ("lux frac smallest")) (f/- ("lux frac smallest"))]
+  [Rev  Order<Rev>  inc dec]
+  )
+
+(do-template [<type> <enum> <top> <bottom>]
+  [(structure: #export _ (Interval <type>)
+     (def: enum <enum>)
+     (def: top <top>)
+     (def: bottom <bottom>))]
+
+  [ Nat Enum<Nat>  (:coerce Nat -1) 0]
+  [ Int Enum<Int>  +9_223_372_036_854_775_807 -9_223_372_036_854_775_808]
+  [Frac Enum<Frac> ("lux frac max") ("lux frac min")]
+  [ Rev Enum<Rev>  (:coerce Rev -1) (:coerce Rev 0)]
+  )
+
 (structure: #export _ (Number Nat)
   (def: + n/+)
   (def: - n/-)
   (def: * n/*)
   (def: / n//)
   (def: % n/%)
-  (def: negate id)
-  (def: abs id)
+  (def: (negate value) (n/- (:: Interval<Nat> top) value))
+  (def: abs function.identity)
   (def: (signum x)
     (case x
       0 0
@@ -88,34 +112,10 @@
   (def: / r//)
   (def: % r/%)
   (def: (negate x) (r/- x (:coerce Rev -1)))
-  (def: abs id)
+  (def: abs function.identity)
   (def: (signum x)
     (:coerce Rev -1)))
 
-(do-template [<type> <order> <succ> <pred>]
-  [(structure: #export _ (Enum <type>)
-     (def: order <order>)
-     (def: succ <succ>)
-     (def: pred <pred>))]
-
-  [Nat  Order<Nat>  inc dec]
-  [Int  Order<Int>  inc dec]
-  [Frac Order<Frac> (f/+ ("lux frac smallest")) (f/- ("lux frac smallest"))]
-  [Rev  Order<Rev>  inc dec]
-  )
-
-(do-template [<type> <enum> <top> <bottom>]
-  [(structure: #export _ (Interval <type>)
-     (def: enum <enum>)
-     (def: top <top>)
-     (def: bottom <bottom>))]
-
-  [ Nat Enum<Nat>  (:coerce Nat -1) 0]
-  [ Int Enum<Int>  +9_223_372_036_854_775_807 -9_223_372_036_854_775_808]
-  [Frac Enum<Frac> ("lux frac max") ("lux frac min")]
-  [ Rev Enum<Rev>  (:coerce Rev -1) (:coerce Rev 0)]
-  )
-
 (do-template [<name> <type> <identity> <compose>]
   [(structure: #export <name> (Monoid <type>)
      (def: identity <identity>)
@@ -177,9 +177,6 @@
   [Frac "lux frac encode" "lux frac decode" "Could not decode Frac"]
   )
 
-## [Values & Syntax]
-(type: Char Nat)
-
 (def: (get-char! full idx)
   (-> Text Nat Char)
   ("lux text char" full idx))
@@ -1011,10 +1008,9 @@
               shifted
               (f/* -1.0 shifted))))))
 
-## [Hash]
 (structure: #export _ (Hash Nat)
   (def: eq Equivalence<Nat>)
-  (def: hash id))
+  (def: hash function.identity))
 
 (structure: #export _ (Hash Int)
   (def: eq Equivalence<Int>)
diff --git a/stdlib/source/lux/data/number/ratio.lux b/stdlib/source/lux/data/number/ratio.lux
index 647eaf4b5..1447040e6 100644
--- a/stdlib/source/lux/data/number/ratio.lux
+++ b/stdlib/source/lux/data/number/ratio.lux
@@ -8,12 +8,13 @@
     monad
     ["p" parser]]
    [data
-    ["E" error]
+    ["." error]
     ["." product]
     ["." maybe]
     [number ("nat/." Codec<Text,Nat>)]
     ["." text ("text/." Monoid<Text>)
      format]]
+   ["." function]
    ["." math]
    ["." macro
     ["." code]
@@ -121,7 +122,7 @@
   (def: (negate (^slots [#numerator #denominator]))
     {#numerator denominator
      #denominator numerator})
-  (def: abs id)
+  (def: abs function.identity)
   (def: (signum x)
     {#numerator 1
      #denominator 1}))
@@ -139,7 +140,7 @@
   (def: (decode input)
     (case (text.split-with separator input)
       (#.Some [num denom])
-      (do E.Monad<Error>
+      (do error.Monad<Error>
         [numerator (nat/decode num)
          denominator (nat/decode denom)]
         (wrap (normalize {#numerator numerator
diff --git a/stdlib/source/lux/function.lux b/stdlib/source/lux/function.lux
index 4d4af846a..ca6ebb73e 100644
--- a/stdlib/source/lux/function.lux
+++ b/stdlib/source/lux/function.lux
@@ -1,24 +1,39 @@
 (.module:
   [lux #*
-   [control [monoid (#+ Monoid)]]])
+   [control
+    [monoid (#+ Monoid)]]])
+
+(def: #export identity
+  {#.doc (doc "Identity function."
+              "Does nothing to it's argument and just returns it."
+              (= (identity "foo")
+                 "foo"))}
+  (All [a] (-> a a))
+  (|>>))
 
 (def: #export (compose f g)
-  {#.doc "Function composition."}
+  {#.doc (doc "Function composition."
+              (= ((compose f g) "foo")
+                 (f (g "foo"))))}
   (All [a b c]
     (-> (-> b c) (-> a b) (-> a c)))
   (|>> g f))
 
 (def: #export (constant value)
-  {#.doc "Create constant functions."}
+  {#.doc (doc "Create constant functions."
+              (= ((constant "foo") "bar")
+                 "foo"))}
   (All [o] (-> o (All [i] (-> i o))))
   (function (_ _) value))
 
 (def: #export (flip f)
-  {#.doc "Flips the order of the arguments of a function."}
+  {#.doc (doc "Flips the order of the arguments of a function."
+              (= ((flip f) "foo" "bar")
+                 (f "bar" "foo")))}
   (All [a b c]
     (-> (-> a b c) (-> b a c)))
   (function (_ x y) (f y x)))
 
 (structure: #export Monoid<Function> (All [a] (Monoid (-> a a)))
-  (def: identity id)
+  (def: identity ..identity)
   (def: compose ..compose))
diff --git a/stdlib/source/lux/host.jvm.lux b/stdlib/source/lux/host.jvm.lux
index 8a6a9f43c..6da77945f 100644
--- a/stdlib/source/lux/host.jvm.lux
+++ b/stdlib/source/lux/host.jvm.lux
@@ -15,7 +15,7 @@
     [collection
      ["." array (#+ Array)]
      ["." list ("list/." Monad<List> Fold<List> Monoid<List>)]]]
-   function
+   ["." function]
    ["." type ("type/." Equivalence<Type>)]
    ["." macro (#+ with-gensyms Functor<Meta> Monad<Meta>)
     ["." code]
@@ -1388,7 +1388,7 @@
                          (spaced (list (super-class-decl$ super)
                                        (with-brackets (spaced (list/map super-class-decl$ interfaces)))
                                        (with-brackets (spaced (list/map constructor-arg$ constructor-args)))
-                                       (with-brackets (spaced (list/map (method-def$ id super) methods))))))]
+                                       (with-brackets (spaced (list/map (method-def$ function.identity super) methods))))))]
     (wrap (list (` ((~ (code.text def-code))))))))
 
 (syntax: #export (null)
@@ -1398,23 +1398,19 @@
 
 (def: #export (null? obj)
   {#.doc (doc "Test for null object reference."
-              (null? (null))
-              "=>"
-              #1
-              (null? "YOLO")
-              "=>"
-              #0)}
+              (= (null? (null))
+                 true)
+              (= (null? "YOLO")
+                 false))}
   (-> (primitive "java.lang.Object") Bit)
   ("jvm object null?" obj))
 
 (syntax: #export (??? expr)
   {#.doc (doc "Takes a (potentially null) ObjectType reference and creates a (Maybe ObjectType) for it."
-              (??? (: java/lang/String (null)))
-              "=>"
-              #.None
-              (??? "YOLO")
-              "=>"
-              (#.Some "YOLO"))}
+              (= (??? (: java/lang/String (null)))
+                 #.None)
+              (= (??? "YOLO")
+                 (#.Some "YOLO")))}
   (with-gensyms [g!temp]
     (wrap (list (` (let [(~ g!temp) (~ expr)]
                      (if ("jvm object null?" (~ g!temp))
@@ -1424,12 +1420,10 @@
 (syntax: #export (!!! expr)
   {#.doc (doc "Takes a (Maybe ObjectType) and returns a ObjectType."
               "A #.None would get translated into a (null)."
-              (!!! (??? (: java/lang/Thread (null))))
-              "=>"
-              (null)
-              (!!! (??? "YOLO"))
-              "=>"
-              "YOLO")}
+              (= (null)
+                 (!!! (??? (: java/lang/Thread (null)))))
+              (= "foo"
+                 (!!! (??? "foo"))))}
   (with-gensyms [g!value]
     (wrap (list (` ({(#.Some (~ g!value))
                      (~ g!value)
diff --git a/stdlib/source/lux/macro/syntax/common/writer.lux b/stdlib/source/lux/macro/syntax/common/writer.lux
index fe4c961e2..3affd97f7 100644
--- a/stdlib/source/lux/macro/syntax/common/writer.lux
+++ b/stdlib/source/lux/macro/syntax/common/writer.lux
@@ -5,6 +5,7 @@
     [collection
      [list ("list/." Functor<List>)]]
     ["." product]]
+   ["." function]
    [macro
     ["." code]]]
   ["." //])
@@ -23,7 +24,7 @@
 
 (def: #export annotations
   (-> //.Annotations Code)
-  (|>> (list/map (product.both code.tag id))
+  (|>> (list/map (product.both code.tag function.identity))
        code.record))
 
 (def: #export type-variables
diff --git a/stdlib/test/test/lux.lux b/stdlib/test/test/lux.lux
index 72b9f45ef..0e41a961c 100644
--- a/stdlib/test/test/lux.lux
+++ b/stdlib/test/test/lux.lux
@@ -6,6 +6,7 @@
    [data
     [number
      ["." i64]]]
+   ["." function]
    ["." math
     ["r" random (#+ Random) ("r/." Functor<Random>)]]
    ["_" test (#+ Test)]]
@@ -21,8 +22,8 @@
     ($_ _.and
         (_.test "Every value is identical to itself."
                 (is? self self))
-        (_.test "The 'id' function doesn't change values in any way."
-                (is? self (id self)))
+        (_.test "The identity function doesn't change values in any way."
+                (is? self (function.identity self)))
         (do @
           [other (r.unicode 1)]
           (_.test "Values created separately can't be identical."
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