--
-- file:    Bindings.lhs
--
-- created: 11/11/96 by Andrew Rock.
--
-- purpose: Defines the ADT Bindings, used to store expressions keyed by name.
--

> module Bindings (Bindings, newBind, updateBind, lookupBind, printBind) where

> import Expr
> import BSTree


> type Bindings = BSTree String Expr


newBind is an empty table of bindings.

> newBind :: Bindings
> newBind = emptyBST


updateBind stores a name-expression pair in the table. Replace

> updateBind :: String -> Expr -> Bindings -> Bindings
> updateBind = updateBST (\ a b -> a)


lookupBind return the expression associated with a name or Undef if not found.

> lookupBind :: String -> Bindings -> Expr
> lookupBind n b
>    = case lookupBST n b of
>         Just e  -> e
>         Nothing -> Undef


printBind pretty prints the names and values.

> printBind :: Bindings -> String
> printBind = unlines . (map s) . flattenBST
>             where s (n,e) = n ++ " = " ++ showExpr e