src/Pure/symtab.ML

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Pure/symtab.ML	Thu Sep 16 12:20:38 1993 +0200
@@ -0,0 +1,114 @@
+(*  Title: 	symtab
+    ID:         $Id$
+    Author: 	Lawrence C Paulson, Cambridge University Computer Laboratory
+    Copyright   1989  University of Cambridge
+*)
+
+(*Unbalanced binary trees indexed by strings
+  No way to delete an entry
+  could generalize alist_of to a traversal functional
+*)
+
+signature SYMTAB = 
+sig
+   type 'a table
+   val alist_of : 'a table -> (string*'a) list
+   val balance : 'a table -> 'a table
+   val lookup : 'a table * string -> 'a option
+   val null : 'a table
+   val is_null : 'a table -> bool
+   val st_of_alist : (string*'a)list * 'a table -> 'a table
+   val st_of_declist : (string list * 'a)list * 'a table -> 'a table
+   val update : (string*'a) * 'a table -> 'a table
+   val update_new : (string*'a) * 'a table -> 'a table
+   exception DUPLICATE of string
+end;
+
+
+functor SymtabFun () : SYMTAB = 
+struct
+
+(*symbol table errors, such as from update_new*)
+exception DUPLICATE of string;
+
+datatype 'a table = Tip  |  Branch of (string * 'a * 'a table * 'a table);
+
+
+val null = Tip;
+
+fun is_null Tip = true
+  | is_null _ = false;
+
+
+fun lookup (symtab: 'a table, key: string) : 'a option = 
+  let fun look  Tip  = None
+	| look (Branch (key',entry,left,right)) =
+	    if      key < key' then look left
+	    else if key' < key then look right
+	    else  Some entry
+  in look symtab end;
+
+(*update, allows overwriting of an entry*)
+fun update ((key: string, entry: 'a), symtab : 'a table)
+  : 'a table =
+  let fun upd  Tip  = Branch (key,entry,Tip,Tip)
+	| upd (Branch(key',entry',left,right)) =
+	    if      key < key' then Branch (key',entry', upd left, right)
+	    else if key' < key then Branch (key',entry',left, upd right)
+	    else                    Branch (key,entry,left,right)
+  in  upd symtab  end;
+
+(*Like update but fails if key is already defined in table.
+  Allows st_of_alist, etc. to detect multiple definitions*)
+fun update_new ((key: string, entry: 'a), symtab : 'a table)
+  : 'a table =
+  let fun upd Tip = Branch (key,entry,Tip,Tip)
+	| upd (Branch(key',entry',left,right)) =
+	    if      key < key' then Branch (key',entry', upd left, right)
+	    else if key' < key then Branch (key',entry',left, upd right)
+	    else  raise DUPLICATE(key)
+  in  upd symtab  end;
+
+(*conversion of symbol table to sorted association list*)
+fun alist_of (symtab : 'a table) : (string * 'a) list =
+  let fun ali (symtab,cont) = case symtab of
+		Tip => cont
+	| Branch (key,entry,left,right) =>
+	    ali(left, (key,entry) :: ali(right,cont))
+  in  ali (symtab,[])  end;
+
+
+(*Make a balanced tree of the first n members of the sorted alist (sal).
+  Utility for the function balance.*)
+fun bal_of (sal, 0) = Tip
+  | bal_of (sal, n) =
+      let val mid = n div 2
+      in  case  drop (mid,sal) of
+	    [] => bal_of (sal, mid)   (*should not occur*)
+	  | ((key,entry):: pairs) =>
+		Branch(key,entry, bal_of(sal,mid), bal_of(pairs, n-mid-1))
+      end;
+
+
+fun balance symtab =
+  let val sal = alist_of symtab
+  in  bal_of (sal, length sal)  end;
+
+
+(*Addition of association list to a symbol table*)
+fun st_of_alist (al, symtab) =
+    foldr update_new (al, symtab);
+
+(*A "declaration" associates the same entry with a list of keys;
+  does not allow overwriting of an entry*)
+fun decl_update_new ((keys : string list, entry: 'a), symtab)
+  : 'a table =
+  let fun decl (key,symtab) = update_new((key,entry), symtab)
+  in  foldr decl (keys, symtab)  end;
+
+(*Addition of a list of declarations to a symbol table*)
+fun st_of_declist (dl, symtab) =
+    balance (foldr decl_update_new (dl, symtab))
+
+end;
+