Add the tiger source code bundle from the book site

Signed-off-by: jmug <u.g.a.mariano@gmail.com>

tiger/chap4/absyn.sml

@@ -0,0 +1,52 @@
+structure Absyn = 
+struct
+
+type pos = int   and   symbol = Symbol.symbol
+
+datatype var = SimpleVar of symbol * pos
+            | FieldVar of var * symbol * pos
+            | SubscriptVar of var * exp * pos
+
+and exp = VarExp of var
+        | NilExp
+        | IntExp of int
+        | StringExp of string * pos
+        | CallExp of {func: symbol, args: exp list, pos: pos}
+        | OpExp of {left: exp, oper: oper, right: exp, pos: pos}
+        | RecordExp of {fields: (symbol * exp * pos) list,
+			typ: symbol, pos: pos}
+        | SeqExp of (exp * pos) list
+        | AssignExp of {var: var, exp: exp, pos: pos}
+        | IfExp of {test: exp, then': exp, else': exp option, pos: pos}
+        | WhileExp of {test: exp, body: exp, pos: pos}
+	| ForExp of {var: symbol, escape: bool ref,
+		     lo: exp, hi: exp, body: exp, pos: pos}
+        | BreakExp of pos
+        | LetExp of {decs: dec list, body: exp, pos: pos}
+        | ArrayExp of {typ: symbol, size: exp, init: exp, pos: pos}
+
+and dec = FunctionDec of fundec list
+        | VarDec of {name: symbol,
+		     escape: bool ref,
+		     typ: (symbol * pos) option,
+		     init: exp,
+		     pos: pos}
+        | TypeDec of {name: symbol, ty: ty, pos: pos} list
+
+and ty = NameTy of symbol * pos
+       | RecordTy of field list
+       | ArrayTy of symbol * pos
+
+and oper = PlusOp | MinusOp | TimesOp | DivideOp
+         | EqOp | NeqOp | LtOp | LeOp | GtOp | GeOp
+
+withtype field = {name: symbol, escape: bool ref, 
+		  typ: symbol, pos: pos}
+   and   fundec = {name: symbol,
+		   params: field list,
+		   result: (symbol * pos) option,
+		   body: exp,
+		   pos: pos}
+     
+end
+