Add Current.x reference page to the docs

gitlab-pages/docs/reference/current.md

@@ -1,6 +1,6 @@
 ---
 id: current-reference
-title: Current
+title: Current - Things relating to the current execution context
 ---
 
 ## Current.balance() : tez
@@ -149,17 +149,87 @@ let check_ = (p: unit) : int =>
 
 <!--END_DOCUSAURUS_CODE_TABS-->
 
-## Current.gas()
-
 ## Current.sender() : address
 
 Get the address that initiated the current transaction.
 
-## Current.address
+<!--DOCUSAURUS_CODE_TABS-->
 
-## Current.self_address
+<!--PascaLIGO-->
+```pascaligo
+function main (const p: unit) : address is sender
+```
 
-## Current.implicit_account
+<!--CameLIGO-->
+```cameligo
+let main (p: unit) : address = Current.sender
+```
+
+<!--ReasonLIGO-->
+```reasonligo
+let main = (p: unit) : address => Current.sender;
+```
+
+<!--END_DOCUSAURUS_CODE_TABS-->
+
+## Current.address(c: a' contract) : address
+
+Get the address associated with a `contract`.
+
+<!--DOCUSAURUS_CODE_TABS-->
+
+<!--PascaLIGO-->
+```pascaligo
+function main (const p : key_hash) : address is block {
+  const c : contract(unit) = implicit_account(p) ;
+} with address(c)
+```
+
+<!--CameLIGO-->
+```cameligo
+let main (p : key_hash) =
+  let c : unit contract = Current.implicit_account p in 
+  Current.address c
+```
+
+<!--ReasonLIGO-->
+```reasonligo
+let main = (p : key_hash) : address => {
+  let c : contract(unit) = Current.implicit_account(p) ;
+  Current.address(c) ;
+};
+```
+
+<!--END_DOCUSAURUS_CODE_TABS-->
+
+## Current.self_address() : address
+
+Get the address of the currently running contract.
+
+<!--DOCUSAURUS_CODE_TABS-->
+
+<!--PascaLIGO-->
+```pascaligo
+function main (const p: unit) : address is self_address
+```
+
+<!--CameLIGO-->
+```cameligo
+let main (p: unit) : address = Current.self_address 
+```
+
+<!--ReasonLIGO-->
+```reasonligo
+let main = (p: unit): address => Current.self_address;
+```
+
+<!--END_DOCUSAURUS_CODE_TABS-->
+
+## Current.implicit_account(p: key_hash) : a' contract
+
+Get the default contract associated with an on-chain keypair. This contract
+doesn't execute code, instead it exists to receive money on behalf of a keys
+owner.
 
 <!--DOCUSAURUS_CODE_TABS-->
 
@@ -180,9 +250,44 @@ let main = (kh: key_hash): contract(unit) => Current.implicit_account(kh);
 
 <!--END_DOCUSAURUS_CODE_TABS-->
 
-## Current.source
+## Current.source() : address
 
-## Current.failwith
+Get the _originator_ of the current transaction. That is, if a chain of transactions
+led to the current execution get the address that began the chain. Not to be confused
+with `Current.sender`, which gives the address of the contract or user which directly
+caused the current transaction.
+
+> ⚠️
+> There are a few caveats you should keep in mind before using `SOURCE` over `SENDER`:
+>
+> 1. SOURCE will never be a contract, so if you want to allow contracts (multisigs etc) to operate your contract, you need to use SENDER
+> 2. https://vessenes.com/tx-origin-and-ethereum-oh-my/ -- in general it is somewhat unsafe to assume that SOURCE understands everything that's going to happen in a transaction. If SOURCE transfers to a malicious (or sufficiently attackable) contract, that contract might potentially transfer to yours, without SOURCE's consent. So if you are using SOURCE for authentication, you risk being confused. A good historical example of this is bakers paying out delegation rewards. Naive bakers did (and probably still do) just use tezos-client to transfer to whatever KT1 delegates they had, even if those KT1 were malicious scripts.
+
+<!--DOCUSAURUS_CODE_TABS-->
+
+<!--PascaLIGO-->
+```pascaligo
+function main (const p: unit) : address is source
+```
+
+<!--CameLIGO-->
+```cameligo
+let main (p: unit) : address = Current.source
+```
+
+<!--ReasonLIGO-->
+```reasonligo
+let main = (p: unit) : address => Current.source;
+```
+
+<!--END_DOCUSAURUS_CODE_TABS-->
+
+## Current.failwith(error_message: string) : a'
+
+Cause the contract to fail with an error message.
+
+> ⚠ Using this currently requires a type annotation on the failwith to unify it
+> with the type of whatever other code branch it's on.
 
 <!--DOCUSAURUS_CODE_TABS-->