Begin removing view related code and docs

lib/base.tri

@@ -119,6 +119,47 @@ maybeBind m f = matchMaybe nothing f m
 maybeOr default m = matchMaybe default id m
 maybe? = matchMaybe false (_ : true)
 
+-- ---------------------------------------------------------------------------
+-- Lazy eliminators
+--
+-- A strict eliminator evaluates both branches because they are ordinary
+-- arguments. Give a branch that recurses, looks something up, or builds
+-- structure to one of these instead: it becomes a thunk and only the selected
+-- branch is ever applied.
+-- ---------------------------------------------------------------------------
+
+lazyBool = (thenK elseK cond :
+  ((chosen : chosen t)
+   (matchBool
+     thenK
+     elseK
+     cond)))
+
+-- This module has no list matcher, so `triage` is used directly: a cons is a
+-- Fork, which is why the cons case sits in the fork slot, exactly as in
+-- `matchList` in lib/list.tri.
+lazyList = (nilK consK xs :
+  ((chosen : chosen t)
+   (triage
+     nilK
+     _
+     (h r : (_ : consK h r))
+     xs)))
+
+lazyMaybe = (noneK someK m :
+  ((chosen : chosen t)
+   (matchMaybe
+     noneK
+     (x : (_ : someK x))
+     m)))
+
+lazyResult = (errK okK result :
+  ((chosen : chosen t)
+   (matchResult
+     (code rest : (_ : errK code rest))
+     (value rest : (_ : okK value rest))
+     result)))
+
 -- ---------------------------------------------------------------------------
 -- Basic arithmetic
 -- ---------------------------------------------------------------------------
@@ -137,18 +178,15 @@ andLazy? = (a bK :
 
 pred = y (self : triage
   0
-  (_ : 0)
+  0
   (bit rest :
-    matchBool
-      (matchBool
+    ifLazy
+      bit
+      (_ : matchBool
+        (t t rest)
         0
-        (pair 0 rest)
-        (equal? rest 0))
-      (matchBool
-        0
-        (pair 1 (self rest))
-        (equal? rest 0))
-      bit))
+        rest)
+      (_ : t (t t) (self rest))))
 
 isZero? = triage true (_ : false) (_ _ : false)
 
@@ -190,6 +228,42 @@ mul = y (self a b :
     (_ : 0)
     (_ : add a (self a (pred b))))
 
+div = y (self a b :
+  ifLazy
+    (isZero? b)
+    (_ : 0)
+    (_ : ifLazy
+      (lt? a b)
+      (_ : 0)
+      (_ : succ (self (sub a b) b))))
+
+mod = y (self a b :
+  ifLazy
+    (isZero? b)
+    (_ : 0)
+    (_ : ifLazy
+      (lt? a b)
+      (_ : a)
+      (_ : self (sub a b) b)))
+
+pow = y (self a b :
+  ifLazy
+    (isZero? b)
+    (_ : 1)
+    (_ : mul a (self a (pred b))))
+
+even? n = (triage
+  true
+  (_ : false)
+  (bit _ : isZero? bit)
+  n)
+
+odd? = (n : not? (even? n))
+
+min = (a b : ifLazy (lte? a b) (_ : a) (_ : b))
+
+max = (a b : ifLazy (lte? a b) (_ : b) (_ : a))
+
 -- ---------------------------------------------------------------------------
 -- Result combinators
 -- ---------------------------------------------------------------------------
@@ -217,7 +291,3 @@ resultMapErr = (f result :
     (code rest : err (f code) rest)
     (value rest : ok value rest)
     result)
-
--- ---------------------------------------------------------------------------
--- View facts
--- ---------------------------------------------------------------------------