REBOL []

money-bag: context [
    data: copy []

    insert: func [value [money!] /local found] [
        repeat i length? data [
            if (first value) = (first data/:i) [
                poke data i add data/:i value
                found: true
                break
            ]
        ]
        if not found [append data value]
    ]

    remove: func [value [money!] /local found] [
        repeat i length? data [
            if (first value) = (first data/:i) [
                poke data i subtract data/:i value
                found: true
                break
            ]
        ]
        if not found [alert "That denomination wasn't found in the bag"]
    ]

    ; no conversions yet.
    total: has [result] [
        result: 0
        foreach value data [result: result + second value]
        result
    ]

    show: does [probe data]
]

ins: func [val] [bag/insert val  bag/show]
rem: func [val] [bag/remove val  bag/show]

bag: make money-bag []
ins $100
ins USD$100
ins DEM$100
ins USD$200
rem $50
print bag/total

halt