Hi Daniel,

A more functional approach might be:

    type Substitution = String -> Maybe Value
    single :: String -> Value -> Substitution
    table  :: Table -> Substitution

    substitute :: Substitution -> Tree -> Tree

For better performance and a lot more features, you could switch to

    type Substitution = Data.Map String Value

- Conal

On Fri, Feb 13, 2009 at 2:40 AM, Daniel Kraft <d@domob.eu> wrote:
Colin Adams wrote:
If you have two functions that do two different things, then they
certainly OUGHT to have different names.

Well, they do "the same thing" but for different arguments; it's like this:

Table is a table of name-value pairs I want to substitute in a tree-like structure using:

substitute :: Table -> Tree -> Tree

For substituting a single name-value pair I want to define this utitlity routine so I don't have to construct a Table all the time in the user code:

substitute :: String -> Value -> Tree -> Tree

In the case I believe it would certainly be good to be able to name both functions the same, but I fear I can not do so?  There are languages where this is explicitelly allowed (e.g. C++ or Java), so I don't think it is such an unuseful or evil thing.


Daniel

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