Helpful library updates

lib/base.tri

@@ -33,6 +33,15 @@ lOr = (triage
 
 matchPair = a : triage _ _ a
 
+fst = p : matchPair (a b : a) p
+snd = p : matchPair (a b : b) p
+
+resultIsOk = result :
+  matchResult (err rest : false) (val rest : true) result
+
+resultIsErr = result :
+  matchResult (err rest : true) (val rest : false) result
+
 not? = matchBool false true
 and? = matchBool id (_ : false)
 
@@ -87,3 +96,94 @@ matchResult = (errCase okCase result :
             tag)
         payload)
     result)
+
+-- ---------------------------------------------------------------------------
+-- Maybe / Option type
+-- ---------------------------------------------------------------------------
+
+nothing = t
+just    = x : t x
+
+matchMaybe = (nothingCase justCase maybe :
+  triage
+    nothingCase
+    justCase
+    (_ _ : nothingCase)
+    maybe)
+
+maybe       = default f m : matchMaybe default f m
+maybeMap    = f m : matchMaybe nothing (x : just (f x)) m
+maybeBind   = m f : matchMaybe nothing f m
+maybeOr     = default m : matchMaybe default id m
+maybe?      = matchMaybe false (_ : true)
+
+-- ---------------------------------------------------------------------------
+-- Basic arithmetic
+-- ---------------------------------------------------------------------------
+
+pred = y (self : triage
+  0
+  (_ : 0)
+  (bit rest :
+    matchBool
+      (matchBool
+        0
+        (pair 0 rest)
+        (equal? rest 0))
+      (matchBool
+        0
+        (pair 1 (self rest))
+        (equal? rest 0))
+      bit))
+
+isZero? = triage true (_ : false) (_ _ : false)
+
+add = y (self x y :
+  triage
+    y
+    (_ : succ y)
+    (_ _ : succ (self (pred x) y))
+    x)
+
+sub = y (self a b :
+  matchBool
+    a
+    (self (pred a) (pred b))
+    (isZero? b))
+
+lt? = a b : not? (isZero? (sub b a))
+lte? = a b : isZero? (sub a b)
+
+mul = y (self a b :
+  matchBool
+    0
+    (add a (self a (pred b)))
+    (isZero? b))
+
+-- ---------------------------------------------------------------------------
+-- Result combinators
+-- ---------------------------------------------------------------------------
+
+mapResult = (f result :
+  matchResult
+    (code rest : err code rest)
+    (value rest : ok (f value) rest)
+    result)
+
+bindResult = (result f :
+  matchResult
+    (code rest : err code rest)
+    (value rest : f value rest)
+    result)
+
+resultOr = (default result :
+  matchResult
+    (_ _ : default)
+    (value _ : value)
+    result)
+
+resultMapErr = (f result :
+  matchResult
+    (code rest : err (f code) rest)
+    (value rest : ok value rest)
+    result)