While

This is an interpreter for the WHILE programming language.

See Releases to get the latest version.

Language

The WHILE programming language features a limited set of operations. Namely these are:

Concatenation

WHILE programs are concatenated via semicolon.

Variable assignment

Variables in WHILE must start with an X and are followed by a natural integer.

x1 = 1;
x2 = 2;
x3 = 3

running this using ./do-while will yield:

| Register | Value |
|----------|-------|
| 1        | 1     |
| 2        | 2     |
| 3        | 3     |

Addition and Subtraction

WHILE programs support the following operations:

x1 = 1;
x2 = 2 + 3;
x3 = x1 + 1;
x4 = x2 + x3

running this using ./do-while will yield:

| Register | Value |
|----------|-------|
| 1        | 1     |
| 2        | 5     |
| 3        | 2     |
| 4        | 7     |

Subtraction is also supported via the infix - operand.

Note that there is no unary -. Negative numbers are supported by subtraction of 0 with a constant, e.g. x1 = 0 - 100.

FOR statement

FOR statements take the current value of the variable and repeat the loop-body accordingly.

x1 = 0;
x2 = 5;
for x2 do
   x1 = x1 + 1
end

will yield:

| Register | Value |
|----------|-------|
| 1        | 5     |
| 2        | 5     |

WHILE statement

WHILE statements repeat their body until your variable reaches 0. Note that WHILE statements may be non-terminating. The only implemented predicate is to repeat until 0.

x1 = 1;
x2 = 0;
while x1 != 0 do
    x2 = 1;
    x1 = 0
end

will yield:

| Register | Value |
|----------|-------|
| 1        | 0     |
| 2        | 1     |

As a matter of fact, the above code produces the same functionality as an IF-statement in other programming languages.

Tooling

Included are the programs do-while and pretty-while.

do-while

do-while will interpret your WHILE programs. If the --input-file myfile.while is provided, program contents are read from there. Otherwise do-while will interpret the program written to stdin.

pretty-while

pretty-while is a code formatter for WHILE programs. Running pretty-while without arguments will prettify the program written to stdin. Supplying --input-file myfile.while formats myfile.while accordingly. If the --write-file flag is provided, the file contents are replaced in the input file, rather than printed to stdout.

arnemileswinter / while