From d177285a761de33b86fcbde72fd718137bfa6f86 Mon Sep 17 00:00:00 2001
From: Xander <xander@biltopia.org>
Date: Thu, 17 Aug 2023 22:08:21 +0200
Subject: Add valid/unvalid type, replacement of optional

---
 kernel/memory/paging.dats |  6 ++++++
 kernel/memory/paging.sats |  2 ++
 lib/DATS/valid.dats       | 15 +++++++++++++++
 lib/SATS/valid.sats       | 18 ++++++++++++++++++
 4 files changed, 41 insertions(+)
 create mode 100644 lib/DATS/valid.dats
 create mode 100644 lib/SATS/valid.sats

diff --git a/kernel/memory/paging.dats b/kernel/memory/paging.dats
index 9b55624..84a8bf4 100644
--- a/kernel/memory/paging.dats
+++ b/kernel/memory/paging.dats
@@ -6,6 +6,7 @@ staload UN = "prelude/SATS/unsafe.sats"
 
 staload "./paging.sats"
 staload "./frame.sats"
+staload "lib/SATS/valid.sats"
 
 assume entry_type = uint64
 
@@ -28,3 +29,8 @@ implement flag_contains(entry,flag) =
       | NO_EXECUTE() => 63
     ))) != zero
 
+(* implement test()  = let *)
+(* in *)
+(*   (5,true) *)
+(* end *)
+
diff --git a/kernel/memory/paging.sats b/kernel/memory/paging.sats
index 784f567..477e942 100644
--- a/kernel/memory/paging.sats
+++ b/kernel/memory/paging.sats
@@ -1,6 +1,7 @@
 #define ENTRY_COUNT 512
 
 staload "./frame.sats"
+staload "lib/SATS/valid.sats"
 
 abstype paddr_type(l:addr) = ptr(l)
 typedef paddr(l:addr) = paddr_type(l)
@@ -31,3 +32,4 @@ fn is_unused(entry_t) : bool
 fn set_unused(&entry_t) : void
 
 fn flag_contains(entry_t,entry_flag) : bool
+fn test() : [b : bool] valid(int,b)
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
+
-- 
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