Add functions and lists

README.md

@@ -19,7 +19,7 @@ Pipple's interpreter provides a REPL for fast prototyping. Try it out by running
 
 ```
 $ ./build/pipple
-pipple> 
+pipple>
 ```
 
 Pipple code you write will be run now. Try something like `(print "Hello, World!")`. See what happens!
@@ -65,6 +65,8 @@ Remember: Polish notation is the key!
 
 ### Conditionals
 
+In Pipple, `nil` is the only non-truthy value. Every non-`nil` value is truthy.
+
 ```
 (let x 0)
 (if (== x 0)
@@ -85,4 +87,34 @@ Remember: Polish notation is the key!
 ```
 (let x (input))
 (print "You said" x)
-```
+```
+
+### Lists
+
+```
+(list item1 item2 item3)
+(list "hi there" 32 nil)
+```
+
+### Functions
+
+Pipple functions require type annotations. They are also first class.
+
+Functions are defined with the following syntax:
+
+`(function returntype [argtype argname argtype argname] (code) (morecode))`
+
+```
+(let x (function int [int x]
+    (return (* x 5))
+))
+
+(print (x 3))
+```
+
+Valid types in Pipple are:
+
+* int
+* double
+* string
+* list