doc: list indexing

Author: Joel Abrahams

README.md

@@ -101,6 +101,34 @@ def factorial(x: Int) -> Int := match x
     ]
 ```
 
+### 🍡 Collections
+
+In mamba sets, lists and maps are first class citizens, they are baked into the language.
+Unlike C-style languages, collection indexes are also a function.
+
+```mamba
+# lists
+def a := [0, 2, 51]
+def b := ["list", "of", "strings"]
+# lists of tuples, buidler syntax
+def ab := [(x, y) | x in a, x > 0, y in b, b != "of" ]
+
+# sets
+def c := { 10, 20 }
+def d := { 3 }
+# sets, builder syntax
+def cd := { x ^ y | x in c, y in d }
+
+# maps
+def e := { "do" => 1, "ree" => 2, "meee" => 3 }
+# maps, builder syntax
+def ef := { x => y - 2 | x in e, y = x.len() }
+
+# indexing works for lists and maps/mappings (sets cannot be indexed because these are unordered)
+print(ab(2)) # prints '(2, "list")'
+print(ef(1)) # prints '1'
+```
+
 ### 📋 Types, Classes, and Mutability
 
 Classes are similar to classes in Python, though we can for each function state whether we can write to `self` or not by stating whether it is mutable or not.

docs/spec/characters.md

@@ -10,8 +10,8 @@ The following is a list of characters in the language
 
 Symbol | Use
 ---|---
-`(` | Denote start of tuple elements or function arguments
-`)` | Denote end of tuple elements or function arguments
+`(` | Denote start of tuple elements or function arguments, including collection indexing (list or mapping)
+`)` | Denote end of tuple elements or function arguments, including collection indexing (list or mapping)
 `{` | Denote start of set, set constructor, or map
 `}` | Denote end of set, set constructor, or map
 `[` | Denote start of list, or opening bracket of generics of a class

docs/spec/grammar.md

@@ -46,7 +46,6 @@ The grammar of the language in Extended Backus-Naur Form (EBNF).
                       | control-flow-expr 
                       | code-block
                       | collection
-                      | index
                       | key-value
                       | operation
                       | anon-fun
@@ -66,7 +65,6 @@ The grammar of the language in Extended Backus-Naur Form (EBNF).
     
     slice            ::= expression ( "::" | "::=" ) expression [ "::" expression ]
     range            ::= expression ( ".." | "..=" ) expression [ ".." expression ]
-    index            ::= expression "[" expression "]"
     
     definition       ::= "def" ( variable-def | fun-def | operator-def )