Can I set the default value for a function argument to be something that's not constant? Example:
tod := Mod[AbsoluteTime[], 86400]
f[x_:tod] := x
In the above, 'tod' changes every time I evaluate it, but "f[]" does not. "?f" yields:
f[x_:42054.435657`11.376386798562935] := x
showing the default value was hardcoded when I created the function.
Is there a workaround here?
It seems to work if the function holds its arguments:
tod := Mod[AbsoluteTime[], 86400]
SetAttributes[f, HoldAll];
f[x_: tod] := x
In[23]:= f[]
Out[23]= 47628.994048
In[24]:= f[]
Out[24]= 47629.048193
Or you can use a construction like the following instead of a default value:
g[] := g[Mod[AbsoluteTime[], 86400]]
g[x_] := x
In[27]:= g[]
Out[27]= 47706.496195
In[28]:= g[]
Out[28]= 47707.842012