MathGroup Archive 2006

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Re: HoldFirst confusion

Yaroslav Bulatov wrote:
> The following gives an error
> f = 5; f[a_] = a
> Set is HoldFirst, so why does it evaluate it's first argument f[a_]?

Conversely, why do the attributes of Set and SetDelayed indicate that they
hold their first argument when the kernel evaluates it.

On a related note, how can you define and use a downvalue that matches
g[1+2] without evaluating the 1+2?

Dr Jon D Harrop, Flying Frog Consultancy Ltd.

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