From 8a629bbbb0bd4950fb0f3c6d14c1a9a0ba057174 Mon Sep 17 00:00:00 2001
From: Eduardo Julian
Date: Sat, 2 Mar 2019 21:09:39 -0400
Subject: Added the capacity to extract type-information from values to create
 new types based on that.

---
 lux-mode/lux-mode.el                             |  2 +-
 stdlib/source/lux/control/thread.lux             |  2 +-
 stdlib/source/lux/tool/compiler/meta/archive.lux |  2 +-
 stdlib/source/lux/type.lux                       |  9 +++++++++
 stdlib/source/test/lux/type.lux                  | 10 ++++++++++
 5 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/lux-mode/lux-mode.el b/lux-mode/lux-mode.el
index 53aecac83..f43034057 100644
--- a/lux-mode/lux-mode.el
+++ b/lux-mode/lux-mode.el
@@ -245,7 +245,7 @@ Called by `imenu--generic-function'."
                     (control//contract (altRE "pre" "post"))
                     ;; Type
                     (type//syntax (altRE "|" "&" "->" "All" "Ex" "Rec" "primitive" "\\$" "type"))
-                    (type//checking (altRE ":" ":coerce" ":~" ":assume" ":of" ":cast" ":share"))
+                    (type//checking (altRE ":" ":coerce" ":~" ":assume" ":of" ":cast" ":share" ":extract"))
                     (type//abstract (altRE "abstract:" ":abstraction" ":representation" ":transmutation" "\\^:representation"))
                     (type//unit (altRE "unit:" "scale:"))
                     (type//poly (altRE "poly:" "derived:"))
diff --git a/stdlib/source/lux/control/thread.lux b/stdlib/source/lux/control/thread.lux
index b83acabc9..c4625d6f5 100644
--- a/stdlib/source/lux/control/thread.lux
+++ b/stdlib/source/lux/control/thread.lux
@@ -7,7 +7,7 @@
    [data
     [collection
      ["." array (#+ Array)]]]
-   [type (#+ :share)
+   [type
     abstract]
    [tool
     [compiler
diff --git a/stdlib/source/lux/tool/compiler/meta/archive.lux b/stdlib/source/lux/tool/compiler/meta/archive.lux
index e34edf0d4..eb9761ab9 100644
--- a/stdlib/source/lux/tool/compiler/meta/archive.lux
+++ b/stdlib/source/lux/tool/compiler/meta/archive.lux
@@ -11,7 +11,7 @@
      format]
     [collection
      ["." dictionary (#+ Dictionary)]]]
-   [type (#+ :share)
+   [type
     abstract]
    [world
     [file (#+ File)]]]
diff --git a/stdlib/source/lux/type.lux b/stdlib/source/lux/type.lux
index 8d0dcad7d..a760180c5 100644
--- a/stdlib/source/lux/type.lux
+++ b/stdlib/source/lux/type.lux
@@ -390,3 +390,12 @@
                          ## TODO: this should use : instead of :assume
                          (:assume (~ (get@ #expression computation))))))]
       (wrap (list (` ((~ shareC) (~ (get@ #expression exemplar)))))))))
+
+(syntax: #export (:extract {type-vars type-parameters}
+                           {exemplar typed}
+                           {extraction s.any})
+  (wrap (list (` (:of (:share [(~+ (list/map code.local-identifier type-vars))]
+                              {(~ (get@ #type exemplar))
+                               (~ (get@ #expression exemplar))}
+                              {(~ extraction)
+                               (:assume [])}))))))
diff --git a/stdlib/source/test/lux/type.lux b/stdlib/source/test/lux/type.lux
index b4796911a..c7daced97 100644
--- a/stdlib/source/test/lux/type.lux
+++ b/stdlib/source/test/lux/type.lux
@@ -166,3 +166,13 @@
           ($_ seq
               <quant-tests>
               )))))
+
+(def: extraction
+  Test
+  (_.test "Can extract types."
+          (let [example (: (Maybe Nat)
+                           #.Nonae)]
+            (type/= (type (List Nat))
+                    (:extract [a]
+                              {(Maybe a) example}
+                              (List a))))))
-- 
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