2 files changed, 33 insertions, 0 deletions
diff --git a/lib/DATS/valid.dats b/lib/DATS/valid.dats
new file mode 100644
index 0000000..f4ea0aa
--- /dev/null
+++ b/lib/DATS/valid.dats
@@ -0,0 +1,15 @@
+#define ATS_DYNLOADFLAG 0
+staload "lib/SATS/valid.sats"
+
+assume valid(a:t@ype,b:bool) = (a,bool b) 
+
+implement{a} create_valid(value : a) = (value,true)
+
+// Create unvalid value by casting null pointer to type.
+implement{a} create_unvalid() = let
+  staload UN = "prelude/SATS/unsafe.sats"
+in
+  ($UN.ptr0_get<a>(the_null_ptr),false) //UNSAFE:
+end
+
+implement{a} unwrap_valid(v) = v.0
diff --git a/lib/SATS/valid.sats b/lib/SATS/valid.sats
new file mode 100644
index 0000000..e3841e0
--- /dev/null
+++ b/lib/SATS/valid.sats
@@ -0,0 +1,18 @@
+
+// implement a type that can be unvalid or valid. 
+// It's a replacement of Optional, but can be allocated on stack, so no heap allocaton needed.
+// When unvalid, it should be not possible to get unvalid value, thats why abstract type is used.
+// bool b: true means valid, false unvalid
+abst@ype valid(a:t@ype,b:bool) = (a,bool b)
+
+typedef Valid(a:t@ype) = [b : bool] valid(a,b) 
+
+// Wraps valid value.
+fn {a:t@ype} create_valid(value : a) : valid(a,true)
+
+// Creates unvalid type.
+fn {a:t@ype} create_unvalid() : valid(a,false)
+
+// Only function that allows getting value. Only accepts valid values. 
+fn {a:t@ype} unwrap_valid(valid(a,true)) : a
+