MathGroup Archive 2006

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: HoldFirst confusion

  • To: mathgroup at
  • Subject: [mg65537] Re: HoldFirst confusion
  • From: Jon Harrop <usenet at>
  • Date: Thu, 6 Apr 2006 06:53:16 -0400 (EDT)
  • References: <e1095n$lkf$>
  • Sender: owner-wri-mathgroup at

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.

  • Prev by Date: Speed: Inner MUCH slower than dot product??
  • Next by Date: Re: HoldFirst question
  • Previous by thread: HoldFirst confusion
  • Next by thread: Re: Re: HoldFirst confusion