From c2577a665818b14adb7b0a0c1eaf326144d4447d Mon Sep 17 00:00:00 2001
From: Eduardo Julian
Date: Sun, 15 Sep 2019 23:17:55 -0400
Subject: Added the ":let" macro to enable reuse of type fragments in larger
 types.

---
 lux-mode/lux-mode.el                        |  3 ++-
 stdlib/source/lux.lux                       | 23 +++++++++++++++++++----
 stdlib/source/lux/control/function/memo.lux |  3 ++-
 3 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/lux-mode/lux-mode.el b/lux-mode/lux-mode.el
index 8f66e2717..ca8178c6a 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" ":by-example" ":hole"))
+                    (type//checking (altRE ":" ":coerce" ":let" ":~" ":assume" ":of" ":cast" ":share" ":by-example" ":hole"))
                     (type//abstract (altRE "abstract:" ":abstraction" ":representation" ":transmutation" "\\^:representation"))
                     (type//unit (altRE "unit:" "scale:"))
                     (type//poly (altRE "poly:" "derived:"))
@@ -433,6 +433,7 @@ This function also returns nil meaning don't specify the indentation."
 (define-lux-indent
   (function 'defun)
   (let 'defun)
+  (:let 'defun)
   (case 'defun)
   (do 'defun)
   (exec 'defun)
diff --git a/stdlib/source/lux.lux b/stdlib/source/lux.lux
index 9cc2254b2..6042457fe 100644
--- a/stdlib/source/lux.lux
+++ b/stdlib/source/lux.lux
@@ -1618,7 +1618,7 @@
                    (wrap (#Cons y ys)))}
                 xs)))
 
-(def:''' (monad/fold m f y xs)
+(def:''' (monad@fold m f y xs)
          #Nil
          ## (All [m a b]
          ##   (-> (Monad m) (-> a b (m b)) b (List a) (m b)))
@@ -1635,7 +1635,7 @@
                  (#Cons x xs')
                  (do m
                    [y' (f x y)]
-                   (monad/fold m f y' xs'))}
+                   (monad@fold m f y' xs'))}
                 xs)))
 
 (macro:' #export (if tokens)
@@ -1770,7 +1770,7 @@
                           [lastO (untemplate lastI)]
                           (wrap (form$ (list (tag$ ["lux" "Cons"]) (tuple$ (list lastO (tag$ ["lux" "Nil"])))))))}
                        lastI)]
-               (monad/fold meta-monad
+               (monad@fold meta-monad
                            (function' [leftI rightO]
                                       ({[_ (#Form (#Cons [[_ (#Identifier ["" "~+"])] (#Cons [spliced #Nil])]))]
                                         (let' [[[_module-name _ _] _] spliced]
@@ -4259,7 +4259,7 @@
                                                   tags)
                                  pattern (tuple$ (list@map identifier$ locals))]
                              (do meta-monad
-                               [enhanced-target (monad/fold meta-monad
+                               [enhanced-target (monad@fold meta-monad
                                                             (function (_ [m-local m-type] enhanced-target)
                                                               (do meta-monad
                                                                 [m-structure (resolve-type-tags m-type)]
@@ -5881,3 +5881,18 @@
   [no    yes]
   [off   on]
   )
+
+(macro: #export (:let tokens)
+  (case tokens
+    (^ (list [_ (#Tuple bindings)] bodyT))
+    (if (multiple? 2 (list@size bindings))
+      (return (list (` (..with-expansions [(~+ (|> bindings
+                                                   ..as-pairs
+                                                   (list@map (function (_ [localT valueT])
+                                                               (list localT (` (..as-is (~ valueT))))))
+                                                   (list@fold list@compose (list))))]
+                         (~ bodyT)))))
+      (..fail ":let requires an even number of parts"))
+
+    _
+    (..fail "Wrong syntax for :let")))
diff --git a/stdlib/source/lux/control/function/memo.lux b/stdlib/source/lux/control/function/memo.lux
index 975d03148..253506508 100644
--- a/stdlib/source/lux/control/function/memo.lux
+++ b/stdlib/source/lux/control/function/memo.lux
@@ -38,7 +38,8 @@
 (def: #export (open memo)
   {#.doc (doc "Memoization where the memoized results can be re-used accross invocations.")}
   (All [i o]
-    (-> (Memo i o) (-> [(Dictionary i o) i] [(Dictionary i o) o])))
+    (:let [Memory (Dictionary i o)]
+      (-> (Memo i o) (-> [Memory i] [Memory o]))))
   (let [memo (//.mixin (//.inherit ..memoization (//.from-recursive memo)))]
     (function (_ [memory input])
       (|> input memo (state.run memory)))))
-- 
cgit v1.2.3