Expand the tutorial section on functions

doc/tutorial/func.md

@@ -40,6 +40,11 @@ not see changes made to these variables after the `lambda` was
 evaluated. `lambda`s can be put in data structures and passed around
 without limitation.
 
+The type of a closure is `lambda(args) -> type`, as opposed to
+`fn(args) -> type`. The `fn` type stands for 'bare' functions, with no
+closure attached. Keep this in mind when writing higher-order
+functions.
+
 A different form of closure is the block. Blocks are written like they
 are in Ruby: `{|x| x + y}`, the formal parameters between pipes,
 followed by the function body. They are stack-allocated and properly
@@ -55,10 +60,25 @@ stored in data structures or returned.
     }
     map_int({|x| x + 1 }, [1, 2, 3]);
 
+The type of blocks is spelled `block(args) -> type`. Both closures and
+bare functions are automatically convert to `block`s when appropriate.
+Most higher-order functions should take their function arguments as
+`block`s.
+
 A block with no arguments is written `{|| body(); }`—you can not leave
 off the pipes.
 
-FIXME mention bind
+## Binding
+
+Partial application is done using the `bind` keyword in Rust.
+
+    let daynum = bind std::vec::position(_, ["mo", "tu", "we", "do",
+                                             "fr", "sa", "su"]);
+
+Binding a function produces a closure (`lambda` type) in which some of
+the arguments to the bound function have already been provided.
+`daynum` will be a function taking a single string argument, and
+returning the day of the week that string corresponds to (if any).
 
 ## Iteration
 

doc/tutorial/lib/codemirror-rust.js

@@ -8,7 +8,8 @@ CodeMirror.defineMode("rust", function() {
     "lambda": "fn", "type": "type", "tag": "tag", "mod": "mod",
     "as": "op", "true": "atom", "false": "atom", "assert": "op", "check": "op",
     "claim": "op", "native": "ignore", "unsafe": "ignore", "import": "else-style",
-    "export": "else-style", "copy": "op", "log": "op", "log_err": "op", "use": "op"
+    "export": "else-style", "copy": "op", "log": "op", "log_err": "op",
+    "use": "op", "bind": "op"
   };
   var typeKeywords = function() {
     var keywords = {"fn": "fn", "block": "fn", "obj": "obj"};

doc/tutorial/syntax.md

@@ -174,8 +174,8 @@ more detail later on (the `T`s here stand for any other type):
 `{fname1: T1, fname2: T2}`
 : Record type.
 
-`fn(arg1: T1, arg2: T2) -> T3`
+`fn(arg1: T1, arg2: T2) -> T3`, `lambda()`, `block()`
-: Function type.  
+: Function types.
 
 `@T`, `~T`, `*T`
 : Pointer types.