Opening up an Expr for easier manipulation

General Usage
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in the relm of metaprogramming: Given an arbitrary well-formed Expr that contains zero or more symbols, to replace each symbol by a value chosen as its referent (given in an available Dict) one assigns into the appropriate Expr.args[n].&tc. Getting there may be half the fun for some … I am wondering if there is a nifty way to open up an Expr so each of its constituent Symbols is available by immediate lookup opened = openup(expr); keys(opened) are the Symbols, values(opened) are the paths into the expr that hold and that may replace the associated key symbol with some other typed value, I realize there needs to be a way to handle symbols that occur more than once – the values may be tuples.
And for this to be helpful, a corresponding unopen( opened ) algorithm is needed.

Is this available?

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It is not very clear what you want to do, perhaps an example would help. But if I understand correctly, you want an expression walker, see

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You might be interested in functions subs() and rewrite() from Espresso.jl.

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thank you for the link … that appears to be less work for me