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Pref::postInput

Actions after input

Use only in the MuPAD Notebook Interface.

This functionality does not run in MATLAB.

Syntax

Pref::postInput(f)
Pref::postInput(NIL)
Pref::postInput()

Description

Pref::postInput allows to set user actions directly after input.

After entering any MuPAD® command x, say, and sending this command to the kernel, f(x) is called before the kernel starts to process the input. This happens for any input until the post-input is switched off via the call Pref::postInput(NIL).

The function f implicitly uses the option hold, i.e., f sees the input command as entered and parsed without any evaluation.

f cannot change the input command that is sent to the kernel for evaluation. However, f can store the input in some global variable for later processing, or some other actions can be performed.

Pref::postInput() returns the current value of the post-input function or NIL, respectively.

Pref::postInput, possibly in conjunction with Pref::postOutput, is useful for initializing variables to compute status information such as the execution time for the command that is to be executed. See Example 2.

Examples

Example 1

The post-input function sees the input as entered, i.e., before evaluation by the kernel:

Pref::postInput(proc() begin 
  print(Unquoted, "input" = args()) 
end):
1 + 2
input = 1 + 2

1 + 2, x = sin(0.1)
input = (1 + 2, x = sin(0.1))

x := 1234; y := 5678
input = (x := 1234)

input = (y := 5678)

Post-input is switched off. This command calls the post-input function for the very last time:

Pref::postInput(NIL):
input = Pref::postInput(NIL)
delete x, y:

Example 2

For any command, the run time is to be computed and displayed. The function declared in Pref::postInput sets a global timer value TIME after each input. After the output of the result, the function declared in Pref::postOutput compares the current time and the starting time TIME.

Pref::postInput(() -> (TIME:= time())):
Pref::postOutput(() -> "Time: ".expr2text((time() - TIME)*msec)):
int(cos(x)*exp(sin(x)), x)

Time: 40 msec 

Time: 40 msec
Pref::postInput(NIL): Pref::postOutput(NIL): 
delete TIME:

Example 3

As another example of using Pref::postInput for storing information to influence the output, we combine it with Pref::output to include (a rendered version of) the input and the result:

Pref::postInput(() -> (LASTINPUT := args())):
Pref::output(() -> val(LASTINPUT) = args()):

This makes MuPAD write "input = result" to the screen, while leaving the history (accessible by %) intact:

int(x, x);
sum((-1)^i/(2*i+1), i=0..infinity);
sin(%)

Parameters

f

The function to be executed after input: a procedure. The default value of this function is NIL (no post-input).

Return Values

Previously set post-input function.

See Also

MuPAD Functions

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