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structure UniqueSymbol :> UNIQUE_SYMBOL =
struct
structure H = HashTable
datatype symbol = SYMBOL of string ref * word
fun equal(SYMBOL(a,_),SYMBOL(b,_)) = a = b
fun compare(SYMBOL(a,_),SYMBOL(b,_)) = String.compare(!a,!b)
fun hash(SYMBOL(_,w)) = w
fun toString(SYMBOL(s,_)) = !s
exception NotThere
fun hashIt(SYMBOL(ref s,_)) = HashString.hashString s
fun eq(SYMBOL(ref x,a),SYMBOL(ref y,b)) = a = b andalso x = y
val table = H.mkTable (hashIt,eq) (117,NotThere)
: (symbol,symbol) H.hash_table
val lookup = H.lookup table
val insert = H.insert table
fun fromString name =
let val s = SYMBOL(ref name,HashString.hashString name)
in lookup s handle _ => (insert(s,s); s) end
end
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