Computer Education in Schools Instruction Language.
This is an interactive programming environment for CESIL, an
educational low-level programming language introduced in the
1970s. You can find out more on the
Wikipedia page.
Select one of these example CESIL programs to load it.
hello.cesil
A hello world program.
timestable.cesil
Print a multiplication table.
polynomial_graph.cesil
Plot a graph of a quartic polynomial.
sinewave.cesil
Plot a graph of a sine wave.
factors.cesil
Calculate the prime factors of a number.
maze.cesil
Generate a psuedorandom maze with a single route.
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Help
CESIL is a very simple low-level programming language,
introduced as a teaching language in the 1970s. It is rather
limited, having only two registers (an integer accumulator
and the program counter) and 14 instructions. It is designed
for batch processing and has no form of interactive or file
input or output. Notable limitations are the lack of any form of
subroutine call, and the absence of any form of indexing or
arrays. However, creative programming can overcome even
these limitations, as illustrated by the "maze"
program on the examples page.
The Wikipedia
page contains a summary of the language, and a brief
reference to the language is available on the
reference card.
Using this application
Programs may be typed directly into the source code editor
window, or loaded from a file on disk by clicking
the Load button and navigating to the file.
Alternatively, one of the example programs can be loaded via
the Load example programs link. Programs
can be saved to disk via the Save button.
The Format button will tidy up the column
alignment of a program, should you wish to. This is done by
converting all indentation to tabs. Tabs are set to 12
characters wide to ensure they are larger than the longest
instructions (SUBTRACT and MULTIPLY).
Before executing a program it must be converted to a runnable form by clicking
Compile. Any errors will be listed in the
output window and highlighted in the source code. Clicking
on the line number in an error message will jump to that
line in the source code.
Once successfully compiled, clicking Run
will execute the program, stopping when a HALT statement or
a breakpoint is encountered. Clicking Run again after
stopping at a breakpoint will continue execution at the next
instruction.
The Step button can be used to execute one
instruction at a time - this can be used from the start of
the program, or after it has been halted via a breakpoint or
use of the Stop button (which will halt a
runaway program).
Breakpoints can be set or cleared by
clicking on a line number in the source code - the line
number will turn red when a breakpoint is set.
The Clear breakpoints button will remove
all breakpoints.
When stopped or single stepping, the next instruction to be
executed will be highlighted in blue.
The Reset button will reset the execution
point to the start of the program (i.e. reset the program
counter to 0).
Whenever the program is stopped, the values of the registers
and variable will be shown in the "Computer state"
window. The program counter is internal but is shown for
completeness.
Code Editor help
The code editor supports normal editing operations such as
cursor and mouse navigation, and cut and paste, using the
standard keys and mouse actions for the browser/operating
system it is running under. It also supports the following:
Find/Replace
Clicking the button (or typing
any of the keyboard shortcuts listed below) will reveal the
Find/Replace bar at the bottom of the screen. This supports
the following functions:
Button
Keyboard
Action
Ctrl-f
Find forwards from the current position.
Ctrl-b
Find backwards from the current position.
Ctrl-r
If a find result is highlighted, replace it with
the replacement text.
Ctrl-d
If a find result is highlighted, replace it with
the replacement text. Then search down for the next
occurrence of the find text.
Ctrl-u
If a find result is highlighted, replace it with
the replacement text. Then search up for the previous
occurrence of the find text.
Ctrl-Shift-F
Set the focus on the find input field.
Ctrl-Shift-R
Set the focus on the replace input field.
Ignore case
Ctrl-Shift-I
Toggle the "Ignore case" option.
Whole words
Ctrl-Shift-O
Toggle the "Whole words" option.
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Escape
Close the find/replace bar.
Deviations from the standard
This CESIL implementation deviates in a few details from the original
ICL CES reference card. In some ways it is more liberal:
Comments may start with ( (as per the
reference card) or * (as seen in
various existing example programs).
Labels and variable names may be more than six
characters long.
It is not necessary to end the program
with *. If present, this will be
treated as a comment and ignored.
Integers are not restricted to the range -8388608 to
+8388607 (i.e. 24 bits) but only by the integer range of
the underlying JavaScript implementation.
Positive integers do not have to start with
a + symbol.
However, it also has a few minor restrictions:
Batch mode is not supported. This means that headers
starting with ** and ending with
*C followed by a program name should not
be used. The ** and *C
will be treated as comments and ignored, but text between
them will be interpreted as instructions, as will the
program name.
The reference card states that comments may be placed on
any line following an instruction and separated by a
space. This is not supported, as it reduces the
reliability of the syntax checker (comments may be
mistaken for operands and vice versa) and does not appear
to be used by any existing example programs so far found.
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Attributions and licenses
All source code for the CESIL application is licensed under the
GPL v3
with the exception of the icons. The sources, licenses and
attributions for the icons are shown below.
Load
Save
Format
Compile
Run
Step
Reset
Stop
Clear breakpoints
Undo
Redo
Search
