Language documentation reflects panic! as a form.

language.md

@@ -387,15 +387,24 @@ This convention also includes anything that prints to the console: `print!`, `re
 Relatedly, just about any function that returns a boolean value is a predicate function--and has a name that ends with a question mark: `eq?` tests for equality; `ref?` tells you if something is a ref or not; `lte?` is less-than-or-equal.
 
 ## Errors: panic! in the Ludus script
-A special function, `panic!`, halts script execution with any arguments output as error messages. Panics also happen in the following cases:
-* a `let` binding has no match against the value of its expression
+A special form, `panic!`, halts script execution with the expression that follows as an error message. 
+
+```
+panic! :oops
+
+if true then :ok else panic! "It's false!"
+```
+
+Panics also happen in the following cases:
+* a `let` binding pattern has no match against the value of its expression
 * a `match` or `when` form has no matching clause
 * a function is called with arguments that do not match any of its clauses
 * something that is not a function or keyword is called as a function
+* a called keyword is partially applied
 * `div` divides by zero
 * certain error handling functions, like `unwrap!` or `assert!`, are invoked on values that cause them to panic
 
-In fact, the only functions in the Prelude which can cause panics are, at current, `div`, `unwrap!`, and `assert!`. And, of course, `panic!` itself.
+In fact, the only functions in the Prelude which can cause panics are, at current, `div`, `unwrap!`, and `assert!`.
 
 ### `nil`s, not errors
 Ludus, however, tries to return `nil` instead of panicking a lot of the time. So, for example, attempting to get access a value at a keyword off a number, while nonsensical, will return `nil` rather than panicking:
@@ -403,9 +412,12 @@ Ludus, however, tries to return `nil` instead of panicking a lot of the time. So
 ```
 let a = true
 a :b :c :d :e &=> nil
+
+let b = [1, 2, 3]
+at (b, 12) &=> nil
 ```
 
 ### Result tuples
-Operations that could fail--especially when you want some information about why--don't always return `nil` on failures. Instead of exceptions or special error values, recoverable errors in Ludus are handled instead by result tuples: `(:ok, value)` and `(:err, msg)`. So, for example, `unwrap!` takes a result tuple and either returns the value in the `:ok` case, or panics in the `:err` case.
+Operations that could fail--especially when you want some information about why--don't always return `nil` on failures. Instead of exceptions or special error values, recoverable errors in Ludus are handled instead by result tuples: `(:ok, value)` and `(:err, msg)`. So, for example, `unwrap!` takes a result tuple and either returns the value in the `:ok` case, or panics in the `:err` case. Or `assert!` will panic on a falsy value; `assert`, instead, returns a result tuple.
 
 Variants of some functions that may have undesirably inexplicit behaviour are written as `{name}/safe`. So, for example, you can get a variant of `div` that returns a result tuple in `div/safe`, which returns `(:ok, result)` when everything's good; and `(:err, "division by zero")` when the divisor is 0. Or, `get/safe` will give you a result rather than returning `nil`. (Althougn `nil` punning makes this mostly unncessary. Mostly.)