[Date Index]
[Thread Index]
[Author Index]
What does FullForm[ ] actually do?
*To*: mathgroup at smc.vnet.net
*Subject*: [mg90467] What does FullForm[ ] actually do?
*From*: AES <siegman at stanford.edu>
*Date*: Thu, 10 Jul 2008 06:35:26 -0400 (EDT)
*Organization*: Stanford University
I'm having trouble grasping just what it is that FullForm[ ] does. For
example:
1) Page 424 of the M5 Book says:
"FullForm[expr] shows the internal form of an
expression in explicit functional notation"
and gives a moderately complex example of this.
I don't find it clearly stated, however, there or anywhere else in the
immediately accessible M5 or M6 documentation, whether executing
"FullForm[expr]" also executes the "expr" itself, although some
experimenting seems to show that it does. If so, perhaps the
documentation ought to make this clear. . . ?
2) Then, just as an example, executing FullForm[y = {a+b}] gives (that
is, Prints, or displays on screen) only the output List[a,b] -- the "y
=" is gone.
But isn't the full expr that's operated on by FullForm, or that forms
the argument of FullForm[expr], the complete expression "y = {a+b}".
That's what fits the stated syntax of the FullForm[expr] command -- and
moreover, page 230 of the M5 Book says:
2.1.1 Everything Is an Expression
"...everything you type into M is treated as an expression."
Isn't the "y = " part typed in as part of expr also? Doesn't it have to
have some form of "internal form"?
3) Even without the "y =" part, suppose we execute either of the inputs
FullForm[y={a+b};] or FullForm[{a+b};] (with a semicolon added).
Either of these gives us back the displayed result "Null" -- but the
first of them also sets the value of y to {a+b}, confirming that the
complete expression inside the FullForm brackets was indeed executed.
But what is it that's "null" here? The "{a+b}" or even the "{a+b};"
part clearly isn't null, since it gets put into y in the first form.
And isn't ";" (the semicolon) also an expression, and also part of the
"{a+b};" expression? ("Everything in M is an expression.") Don't both
; and {a+b}; have to have an internal form?
The bottom line seems to be that FullForm[{a+b}], when executed, in some
cases does as claimed "show the internal form of that expression in
explicit functional notation."
However, the FullForm[{a+b};] or FullForm[y={a+b};] examples seem to
show that executing FullForm[expr] returns the result of executing that
expr, not the expression itself . . . ?
Prev by Date:
**Re: Display[ ] renewed?**
Next by Date:
**Re: Coupled second-order nonlinear ODEs**
Previous by thread:
**Glitch in Exporting PDFs from Mathematica to Illustrator, one solution**
Next by thread:
**Re: What does FullForm[ ] actually do?**
| |