Add rough draft documentation for hashing keys and pack/unpack operations

gitlab-pages/docs/language-basics/tezos-specific.md

@@ -0,0 +1,80 @@
+---
+id: tezos-specific
+title: Tezos Domain-Specific Operations
+---
+
+LIGO is a language for writing Tezos smart contracts. It would be a little odd if
+it didn't have any Tezos specific functions. This page will tell you about them.
+
+## Pack and Unpack
+
+Michelson provides the `PACK` and `UNPACK` instructions for data serialization.
+`PACK` converts Michelson data structures to a binary format, and `UNPACK`
+reverses it. This functionality can be accessed from within LIGO.
+
+> ⚠️ There should be a message here about the dangers of using `UNPACK` on untrusted
+data, perhaps about executable code?
+
+<!--DOCUSAURUS_CODE_TABS-->
+
+<!--PascaLIGO-->
+```pascaligo
+function id_string (const p : string) : option(string) is block {
+  const packed : bytes = bytes_pack(p) ;
+} with (bytes_unpack(packed): option(string))
+```
+
+<!--CameLIGO-->
+```cameligo
+let id_string (p: string) : string option =
+  let packed: bytes = Bytes.pack p in
+  ((Bytes.unpack packed): string option)
+```
+
+<!--ReasonLIGO-->
+```reasonligo
+let id_string = (p: string) : option(string) => {
+  let packed : bytes = Bytes.pack(p);
+  ((Bytes.unpack(packed)): option(string));
+};
+```
+
+<!--END_DOCUSAURUS_CODE_TABS-->
+
+## Hashing Keys
+
+<!--DOCUSAURUS_CODE_TABS-->
+
+<!--PascaLIGO-->
+```pascaligo
+function check_hash_key (const kh1 : key_hash; const k2 : key) : bool * key_hash is block {
+  var ret : bool := False ;
+  var kh2 : key_hash := crypto_hash_key(k2) ;
+  if kh1 = kh2 then ret := True else skip; 
+} with (ret, kh2)
+```
+
+<!--CameLIGO-->
+```cameligo
+let check_hash_key (kh1, k2: key_hash * key) : bool * key_hash =
+  let kh2 : key_hash = Crypto.hash_key k2 in
+  if kh1 = kh2
+  then (true, kh2)
+  else (false, kh2)
+```
+
+<!--ReasonLIGO-->
+```reasonligo
+let check_hash_key = (kh1_k2: (key_hash, key)) : (bool, key_hash) => {
+  let kh1, k2 = kh1_k2;
+  let kh2 : key_hash = Crypto.hash_key(k2);
+  if (kh1 == kh2) {
+    (true, kh2);
+  }
+  else {
+    (false, kh2);
+  }
+};
+```
+
+<!--END_DOCUSAURUS_CODE_TABS-->

gitlab-pages/website/sidebars.json

@@ -11,7 +11,8 @@
       "language-basics/loops",
       "language-basics/unit-option-pattern-matching",
       "language-basics/maps-records",
-      "language-basics/sets-lists-touples"
+      "language-basics/sets-lists-touples",
+      "language-basics/tezos-specific"
     ],
     "Advanced": [
       "advanced/timestamps-addresses",