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Babbage Lite Syntax

Once again, the Analytical Engine taught by my professor was simplified for lecture and brevity which resulted in me making Babbage Lite. Babbage Lite programs contain the following:

Number Cards

N<address> <value>

Declares a constant or variable in the specified address of store. Value is the initial value stored.

  • Allowable addresses are only from 0 to 999.
  • By default, values of all addresses in store is 0.

Examples:

N000 0
N111 1
N5   8

Variable Cards

Load

L<address>

Loads the value from the specified address of store into the mill.

  • Two loads supply the left (first ingress axis) and right (second ingress axis) operands of arithmetic operations.

Example:

L1
L2

Store

S<address>

Stores from the egress axis (mill’s result) into the specified address of store.

Example:

S3

Operation Cards

+   . addition
-   . subtraction
*   . multiplication
/   . division
%   . modulo

Sets the arithmetic operation to be performed.

Example:

+
L1  . load into the first ingress axis
L2  . load into the second ingress axis
S3  . store from egress axis into store `003`

Action Cards

Print

P

Prints the value from the egress axis (mill's result).

Bell

B

Rings a bell.

Halt

H

Halts the machine.

Combinatorial Cards

Unconditional Jump

CF+<skips>   . jump forward skips + 1 (from current line) cards
CB+<skips>   . jump backward skips - 1 (from current line) cards

Why the + 1/- 1? To put it simply, the reader must move for a card to be read.

At least, that's what I remember my professor telling us.

Conditional Jump

CF?<skips>  . jump forward skips + 1 (from current line) cards if the run-up lever is set
CB?<skips>  . jump backward skips - 1 (from current line) cards if the run-up lever is set

Run-up Lever is set/unset on every arithmetic operation:

  • Addition: Run-up Lever only when sign differs between the first ingress axis and egress axis.
  • Subtraction: Run-up Lever sets only when sign differs between the first ingress axis and egress axis.
  • Division: Run-up Lever sets only when the divisor is 0.
  • Multiplication: Run-up Lever never sets.
  • Modulo: Run-up Lever sets only when the divisor is 0.

Quick Mental Model

-
x
y
CF/CB+/?...

is roughly equivalent to:

  • If x is non-negative:
    • If x < y, then CF/CB+/?...
  • If x is negative:
    • If x ≥ y, then CF/CB+/?...

Helpful Tips

Common Patterns

DO-WHILE

Example:

N0 5    . counter
N1 1    . constant 1
N2 0    . constant 0

# DO { ...
-
L0
L1
S0
P
-
L2
L0
CB?9
# ... } WHILE (0 < counter)

H
  • N2 0 is only helpful in outlining your intentions as 002 is already 0, by default (as with all addresses).
  • 0 < counter only works as a mental model because 0 is non-negative.