Re: MakeExpression
- To: mathgroup at smc.vnet.net
- Subject: [mg33639] Re: MakeExpression
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Thu, 4 Apr 2002 19:39:59 -0500 (EST)
- Organization: Universitaet Leipzig
- References: <a8g2di$b0t$1@smc.vnet.net>
- Reply-to: kuska at informatik.uni-leipzig.de
- Sender: owner-wri-mathgroup at wolfram.com
Hi,
a_Plus in your definition is nonsense. A head Plus
would require, that a *is* already an expression, but
that can't be the case, because MakeExpression[] is called
to *make* the expression. A RowBox[] *can* only have strings/boxes
in it's list argument and
MakeExpression[
RowBox[{"\[FilledCircle]", "[", b__, "]"}], StandardForm] :=
MakeExpression[RowBox[{"{", b, "}"}], StandardForm]
will parse
\[FilledCircle][1, 2, 3, 4]
inputs as list {1, 2, 3, 4} *and* has a pattern b__
Hers is an example
MakeExpression[
RowBox[{RowBox[{"(", a_, ")"}], "[", c___, "]"}], fmt_:StandardForm] :=
MakeExpression[RowBox[{"\[FilledCircle]", "[", c, "]"}], StandardForm]
that will tranform any combination of (anything)[aSequence] to
\[FilledCircle][sequence]
Regards
Jens
Dustin Vink wrote:
>
> Dear Reader,
>
> Consider the following Mathematica problem. How does one incorporate
> pattern matching conditions with the command MakeExpression?
>
> The following does NOT work:
>
> MakeExpression[RowBox[{a_Plus, "[", b__, "]"}], StandardForm] :=
> MakeExpression[a, StandardForm]
>
> Any form of condition used at the lhs seems to be ignored.