XEQ: compile and execute a character string (H)

- result = XEQ(string [, *error_label] )
executes string under script control
- string must be a ⇒ valid expression
- *error_label is an optional label to jump to if an error occurs. Without this label an error message is shown in the error case.
- string is translated and executed only when XEQ is called
- variables of the current script procedure can be used. Non existent variables are allocated while the string is executed and deallocated then
- XEQ
  will not execute
  GOTO or multiline constructs like DO, CALL, IF..THEN
- string can be generated by the script, it can be stored in a file to be recalled later
the toolbar tool 1+1 is an example how XEQ works and what it can do. Copy (Ctrl+C) and paste (Ctrl+V) to script i you like.
examples:
- - result = XEQ( "a = b + c" )
  a is set only if it is available in the calling procedure, else "b + c" is stored in result
- - x = XEQ( "CALL my_subroutine", *999) ! will jump to ⇒ label 999
- execute 1 command out of a filed list:
  - OPEN(FIle="my_list.txt")
  - READ(FIle="my_list.txt", Row=6) string
  - XEQ(string) ! executes row 6 of file my_list.txt