Re: Determine if a parameter is a function

• To: mathgroup at smc.vnet.net
• Subject: [mg101818] Re: Determine if a parameter is a function
• From: Peter Breitfeld <phbrf at t-online.de>
• Date: Sat, 18 Jul 2009 04:50:18 -0400 (EDT)
• References: <h3kddu\$g35\$1@smc.vnet.net> <h3pekf\$o0s\$1@smc.vnet.net>

```With the help of Valerie Astanoff I ended up with the following
function, which tests, if f is not a Function and sends an Abort[] in
this case:

NoFunc::nofun = "Parameter  `1`  muss eine Funktion sein.";
NoFunc[f_] :=
((DownValues[f] =!= {}) || (Attributes[f] =!= {})))],
Message[kF::nofun, f]; Abort[]]

Valeri Astanoff wrote:

> On 15 juil, 13:09, Peter Breitfeld <ph... at t-online.de> wrote:
>> Suppose I have a function eg
>>
>> myfunc[f_,x_]:= <some definitions>
>>
>> f should be a pure function like (#^2&) or Function[{x},x^2] or a named
>> function either self defined, like
>>
>> f[x_]:=x^2   or g[x_]=x^2
>>
>> or built-in like Sin, Log, ...
>>
>> How can I test if f is any of these, to be able to yield a message on
>> wrong input?
>>
>> I found that the pure-functions have Head Function, but all the others
>>
>> --
>> _________________________________________________________________
>> Peter Breitfeld, Bad Saulgau, Germany --http://www.pBreitfeld.de
>
>
> Good day,
>
> This way to do it should be ok for almost all non-pathological cases :
>
> In[1]:= myfunc::nfun="argument `1` should be a function.";
>
> In[2]:= myfunc[(f_?NumericQ|f_List|f:(True|False)),x_]:=
> (Message[myfunc::nfun,f]; HoldForm@myfunc[f,x]);
>
> myfunc[f_Symbol /; DownValues[f]=={} && Attributes[f]=={},x_]:=
> (Message[myfunc::nfun,f]; HoldForm@myfunc[f,x]);
>
> myfunc[f_,x_]=f[x];
>
>
> A few tests :
>
> In[5]:= f1=#^2&;
>
> In[6]:= f2[x_]=x^2;
>
> In[7]:= f3=Function[{x},x^2];
>
> In[8]:= myfunc[f1,x]
> Out[8]= x^2
>
> In[9]:= myfunc[f2,x]
> Out[9]= x^2
>
> In[10]:= myfunc[f3,x]
> Out[10]= x^2
>
> In[11]:= myfunc[ff,x]
>  myfunc::nfun: argument ff should be a function.
> Out[11]= myfunc[ff,x]
>
> In[12]:= myfunc[1,x]
>  myfunc::nfun: argument 1 should be a function.
> Out[12]= myfunc[1,x]
>
> In[13]:= myfunc[{1,2},x]
>  myfunc::nfun: argument {1,2} should be a function.
> Out[13]= myfunc[{1,2},x]
>
> In[14]:= myfunc[True,x]
>  myfunc::nfun: argument True should be a function.
> Out[14]= myfunc[True,x]
>
> In[15]:= myfunc[Sin,x]
> Out[15]= Sin[x]
>
> --
> V.Astanoff
>

--
_________________________________________________________________
Peter Breitfeld, Bad Saulgau, Germany -- http://www.pBreitfeld.de

```

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