idlwave: Examining Variables
5.5 Examining Variables
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Do you find yourself repeatedly typing, e.g., ‘print,n_elements(x)’, and
similar statements to remind yourself of the
type/size/structure/value/etc. of variables and expressions in your code
or at the command line? IDLWAVE has a suite of special commands to
automate these types of variable or expression examinations. They work
by sending statements to the shell formatted to include the indicated
expression, and can be accessed in several ways.
These _examine_ commands can be used in the shell or buffer at any
time (as long as the shell is running), and are very useful when
execution is stopped in a buffer due to a triggered breakpoint or error,
or while composing a long command in the IDLWAVE shell. In the latter
case, the command is sent to the shell and its output is visible, but
point remains unmoved in the command being composed: you can inspect the
constituents of a command you’re building without interrupting the
process of building it! You can even print arbitrary expressions from
older input or output further up in the shell window; any expression,
variable, number, or function you see can be examined.
If the variable ‘idlwave-shell-separate-examine-output’ is non-‘nil’
(the default), all examine output will be sent to a special ‘*Examine*’
buffer, rather than the shell. The output of prior examine commands is
saved in this buffer. In this buffer <c> clears the contents, and <q>
hides the buffer.
The two most basic examine commands are bound to ‘C-c C-d C-p’, to
print the expression at point, and ‘C-c C-d ?’, to invoke help on this
expression(1). The expression at point is either an array expression or
a function call, or the contents of a pair of parentheses. The chosen
expression is highlighted, and simultaneously the resulting output is
highlighted in the shell or separate output buffer. Calling the above
commands with a prefix argument will use the current region as
expression instead of using the one at point. which can be useful for
examining complicated, multi-line expressions. Two prefix arguments
(‘C-u C-u C-c C-d C-p’) will prompt for an expression to print directly.
By default, when invoking print, only an initial portion of long arrays
will be printed, up to ‘idlwave-shell-max-print-length’.
For added speed and convenience, there are mouse bindings which allow
you to click on expressions and examine their values. Use ‘S-mouse-2’
to print an expression and ‘C-M-mouse-2’ to invoke help (i.e., you need
to hold down <META> and <CONTROL> while clicking with the middle mouse
button). If you simply click, the nearest expression will be selected
in the same manner as described above. You can also _drag_ the mouse in
order to highlight exactly the specific expression or sub-expression you
want to examine. For custom expression examination, and the powerful
customizable pop-up examine selection, 
Custom Expression
Examination.
The same variable inspection commands work both in the IDL Shell and
IDLWAVE buffers, and even for variables at higher levels of the calling
stack. For instance, if you’re stopped at a breakpoint in a routine,
you can examine the values of variables and expressions inside its
calling routine, and so on, all the way up through the calling stack.
Simply step up the stack, and print variables as you see them (
Walking the Calling Stack, for information on stepping back through
the calling stack). The following restrictions apply for all levels
except the current:
• Array expressions must use the ‘[ ]’ index delimiters. Identifiers
with a ‘( )’ will be interpreted as function calls.
• N.B.: printing values of expressions on higher levels of the
calling stack uses the _unsupported_ IDL routine ‘ROUTINE_NAMES’,
which may or may not be available in future versions of IDL.
Caveat Examinor.
-- User Option: idlwave-shell-expression-face
The face for ‘idlwave-shell-expression-overlay’. Allows you to
choose the font, color and other properties for the expression
printed by IDL.
-- User Option: idlwave-shell-output-face
The face for ‘idlwave-shell-output-overlay’. Allows to choose the
font, color and other properties for the most recent output of IDL
when examining an expression."
-- User Option: idlwave-shell-separate-examine-output (‘t’)
If non-‘nil’, re-direct the output of examine commands to a special
‘*Examine*’ buffer, instead of in the shell itself.
-- User Option: idlwave-shell-max-print-length (200)
The maximum number of leading array entries to print, when
examining array expressions.
---------- Footnotes ----------
Debug Mode::)
Info Catalog
idlwave: Debugging IDL Programs
idlwave: The IDLWAVE Shell
idlwave: Custom Expression Examination