ESI(ID:404/esi001)

Engineering and Scientific Interpreter  

Sample conversations with the  Engineering and  Scientific Interpreter David J. Waks Applied Data Research Princeton  N.J.

I. Samples of  direct statements:


II. Use of indirect statements to compute the area and circumference of a circle, given its radius.



Notes on the Conversations

(1) A back arrow  (<-) is typed whenever ESI wants the user to "say" something.  Thus any line beginning with a back arrow was typed by  the user; any without the back arrow, by the computer.

(2) "DELETE ALL" commands  ESI to clear user storage of everything associated with the preceding user program.

(3) "TYPE" commands the evaluation and typing out of one or  more arithmetic expressions.

(4) All results are stored and presented as decimal numbers with exactly seven decimal digits of precision.

(5) The SGN function is the "sign" or "signum" function of mathematics.

(6) A variable, such as "Y" here, which has not been set to any value is considered to be "undefined" and any use of  it in an arithmetic expression  is flagged as an error.

(7) Every statement in ESI is an English sentence, and must end in a period.

(8) This command  is meaningless, since "XY" is not a valid name for a variable  (the only valid  names are the single letters A through Z), and the multiplication sign is  missing if the intention was to evaluate the product of "X" and "Y".

(9) The single letter "E"  means "times ten to the."  Thus 3E-40 is ESI's notation for 3 x 10^-40

(10) All numbers  stored by ESI must be in the range of 10^-63   to 10⁶³.  The number  "A^2" is out  of this range.

(11) ESI treats any attempt to divide by zero, including 0/0, as an error.

(12) In this iterative statement, "I" will take on values beginning with 2, in increments of 3, until 5; i.e., 2 and 5.

(13) "A" has already been assigned a value as an unsubscripted variable.  It cannot simultaneously be subscripted and unsubscripted.

(14) "DELETE" commands ESI to make the variable "undefined."  It can now be used with a subscript. Note that no declaration  (such as DIMENSION) is required before using a variable with subscripts.

(15) A more complicated example of subscripting; the subscript expression is R/2.

(16) "TYPE ALL VALUES" commands ESI to type out the values of all defined variables.

(17) Note that the values of "I" and "R", after the completion of iterative statements involving them, are not the terminal values specified by the FOR statement.

(18) If a number is typed preceding a statement, the statement is not executed immediately, but is stored away associated with that number, called its "step number."

(19) "DO STEP" commands the execution of a previously stored step.

(20) "DEMAND" (here being executed by step 1.1) requests from the user a value for the indicated variable  (in this case "R").  Note that the back arrow  (<--) again indicates that ESI has given control of the Teletype to the user.

(21) Previous "TYPE" statements illustrated the typing of evaluated arithmetic expressions  (TYPE X*Y.) and character strings  (TYPE "THAT'S RIGHT".).  This example illustrates how a single TYPE statement may mix these two forms.  Character strings in quotes alternate with arithmetic expressions (in this case, note that R, A, and C are very trivial arithmetic expressions).

(22) The digit preceding the decimal point in a step number is called the part number, and must be in the range of 1 to 9.  All steps with the same part number are considered to be a part of a program. The "DO PART" command causes each step of the part to be executed in step number order.  At the end of execution of the last step (the one with the highest numerical step number),  control returns to the step following the "DO PART" if it was executed from an indirect (stored) statement or to the user if it was executed as a direct statement (from the Teletype).

(23) We forgot to give a definition for P.  Note that the error was not detected until the statement was executed.

(24) This illustrates an abbreviated form of the "SET" statement which can only be used as a direct statement (executed immediately rather than being stored away).  P is, of course,  Pi.

(25) "TO STEP" causes the designated step to be executed next, rather than the next step in step number order.  Note that step 1.5 is inserted following step 1.4, causing the entire program to be a five-step loop.

(26) At any time during the execution of a program, the "ALT MODE" key on the Teletype can be typed.  At the end of execution of the current step, the execution of the program is interrupted and an appropriate message is typed.  When execution is suspended, the only legitimate statements are GO, CANCEL, and TYPE.
(27) "GO" commands that the interrupted program be continued where it left off.

(28) The user may type any arithmetic expression in response to a "DEMAND" but must make sure that only defined variables are used in the expression.

(29) "CANCEL" commands that the execution of the program be cancelled.  It cannot now be continued with GO.

(30) At this point, we have decided to evaluate the area and circumference for a given range of values of the radius.  We therefore delete the DEMAND statement and insert an iterative statement as part 2.

(31) We forgot to delete step 1.5, which now refers to a non-existent step number.

(32) "TYPE ALL" commands the typing of everything currently stored by ESI ? that is, all steps and all values.

(33) The user can type "RUBOUT" to delete a typing error.  Each "RUBOUT" deletes one character and types a back arrow to indicate this. Any number of characters can be deleted this way; if "RUBOUT" is typed with the input line completely empty (all characters rubbed out), the bell is rung.

Close
Example