subst.sml

| Let(dec1::decs, e2) => (case dec1 of 
		Val(expr,name) => if name = x then
				Let(Val(subst s expr,name)::decs,e2)	
				else
				let
				val (varName,Let(rnDecs, rnExpr)) = if member name (freeVars e') 
					then rename (name,Let(decs, e2)) else (name,Let(decs, e2))
				val Let(subDecs,subExpr) = subst s (Let(rnDecs, rnExpr))
				in
					Let(Val(subst s expr,varName)::subDecs,subExpr)
				end				
|ByName(expr,name) => if name = x then
				Let(ByName(subst s expr,name)::decs,e2)	
				else
				let
				val (varName,Let(rnDecs, rnExpr)) = if member name (freeVars e') 
					then rename (name,Let(decs, e2)) else (name,Let(decs, e2))
				val Let(subDecs,subExpr) = subst s (Let(rnDecs, rnExpr))
				in
					Let(ByName(subst s expr,varName)::subDecs,subExpr)
				end	
|Valtuple(expr,li) => if List.exists (fn name=>name=x) li then
				Let(Valtuple(subst s expr,li)::decs,e2)
				else
				let
				val (rnLi,Let(rnDecs, rnExpr)) = List.foldl (fn (name',(l,Let(d,e)))=>
					let
					val (varName,Let(d',e')) = if member name' (freeVars e')
						then rename  (name',Let(decs,e2)) else (name',Let(decs, e2))
					in
						(l@[varName],Let(d',e'))
					end) ([],Let(decs,e2)) li
				val Let(subDecs,subExpr) = subst s (Let(rnDecs, rnExpr))
				in
					Let(Valtuple(subst s expr,rnLi)::subDecs,subExpr)
				end)