ibdp-classes 0.6.0
An interpreter for pseudocode similar to that used in IBDP Computer Science courses.
Requires Python: >=3.12

# IBDP Computer Science Pseudocode Classes

The IB Computer Science documents, *Approved notation for developing pseudocode* and *Pseudocode in Examinations*, describe pseudocode and a set of limited-functionality *array*, *collection*, *stack* and *queue* data structure classes that may come up and be used in exams.

This is a simple Python implementation of an IB pseudocode interpreter and the above restrictive classes, which can be used in programming activities to help familiarize students with the pseudocode and classes.

Under the hood, the classes are simple wrappers over a Python list and the interpreter simply runs some perfunctory tests, translates pseudocode into (really ugly) Python and then does its best to execute the translation and generate helpful error messages.

You can submit [issues and requests here](https://github.com/ram6ler/ibdp_classes/issues).

## Install

```text
python -m pip install ibdp-classes
````

## Interpreting IB pseudocode

We can use the library to interpret pseudocode. For example:

`example.pseudocode`

```text
output "Collection..."
ITEMS = new Collection(1, 2, 3)
ITEMS.resetNext()
loop while ITEMS.hasNext()
    X = ITEMS.getNext()
    output "X =", X
end loop
```

At the command line:

```text
python -m ibdp_classes example.pseudocode
```

Output:

```text
Collection...
X = 1
X = 2
X = 3
```

We can also interpret IB pseudocode from within a Python script by creating and calling a `Pseudocode` instance. For example:

```python
import ibdp_classes as ib

code = """
output "Array..."
XS = new Array(1, 2, 3, 4, 5)
N = 5
loop I from 0 to N - 1
    output "xs[", I, "] = ", XS[I]
end loop
"""

script = ib.Pseudocode(code)
output = script()
print(output)
```

Output:

```txt
Array...
xs[ 0 ] =  1
xs[ 1 ] =  2
xs[ 2 ] =  3
xs[ 3 ] =  4
xs[ 4 ] =  5
```

## Additions to IB pseudocode

### `function` and `procedure`

In exams, IB pseudocode typically uses `output` to display results, and either doesn't explicitly define functions or procedures, or else does so informally and inconsistently. I have thus added `function` and `procedure` structures to the pseudocode definitions.

For example:

```text
function CONTAINS(NEEDLE, HAYSTACK, N)
    // Where NEEDLE is a string, HAYSTACK is an Array
    // of strings, and N is the length of HAYSTACK.
    FOUND = false
    loop K from 0 to N-1
        if HAYSTACK[K] = NEEDLE then
            FOUND = true
        end if
    end loop
    return FOUND
end function

HAYSTACK = new Array(20, -3, 5, 7, 2, 13, 12, 19)
output "HAYSTACK:", HAYSTACK

output "5 is in HAYSTACK?"
output CONTAINS(5, HAYSTACK, 8)

output "4 is in HAYSTACK?"
output CONTAINS(4, HAYSTACK, 8)
```

Output:

```text
HAYSTACK: Array { 20, -3, 5, 7, 2, 13, 12, 19 }
5 is in HAYSTACK?
True
4 is in HAYSTACK?
False
```

### Input types using `as`

In IBDP pseudocode, the keyword `input` is used to generically collect input from the user, and context is used to determine whether the input should be interpreted as a string, integer or floating point number. I have added `as int` and `as float` as appendages to the input statement for when we want to be explicit.

For example:

```text
output "Input an integer."
input COUNT as int

if COUNT mod 2 = 0 then
    output COUNT, "is even..."
else
    output COUNT, "is odd..."
end if
```

## Importing functionality

If we would like to give the pseudocode access to variables or functions defined in Python, we can pass the definitions as a dictionary when calling the `Pseudocode` instance:

```python
from random import random
from math import floor
import ibdp_classes as ib

code = """
loop I from 1 to 10
    output I, ":", FLOOR(10 * RANDOM())
end loop
"""

script = ib.Pseudocode(code)
output = script({"FLOOR": floor, "RANDOM": random})
print(output)
```

Example output:

```text
1 : 5
2 : 1
3 : 9
4 : 9
5 : 7
6 : 0
7 : 4
8 : 1
9 : 7
10 : 0
```

Alternatively, we can have the pseudocode in its own file and the definitions we want available in a separate Python file, and then set `-defs` to the name of the Python file when we interpret the pseudocode from the command line. For example:

`defs.py`

```python
from random import random
from math import floor

RANDOM = random
FLOOR = floor
```

`example.pseudo`

```text
loop I from 1 to 10
    output I, ":", FLOOR(10 * RANDOM())
end loop
```

From the command line:

```text
python -m ibdp_classes -defs defs.py example.pseudo
```

Example output:

```text
1 : 5
2 : 8
3 : 4
4 : 3
5 : 1
6 : 5
7 : 3
8 : 2
9 : 3
10 : 5
```

## Extensions

In addition to being able to add bespoke functionality using `-defs`, a few wrappers are available as extensions that are not defined by IB but that can be helpful in certain lesson scenarios. We can access these extensions using `-ext` and passing a string of extensions we would like to expose the pseudocode to.

Extensions available:

### `strings`

The `strings` extension exposes the following functions, which can helpful in activities involving string searches and manipulation.

* `SUBSTRING(STRING, START, END)`

  The substring of `STRING` starting at index `START` (inclusive) and ending at index `END` (exclusive).

* `CHARACTER(STRING, INDEX)`

  The character in `STRING` at index `INDEX`.

* `UPPERCASE(STRING)` and `LOWERCASE(STRING)`

  The uppercase and lowercase respectively of `STRING`.

* `REPLACE(STRING, OLD, NEW)`

  A copy of `STRING` with `OLD` replaced with `NEW`.

* `CONTAINS(STRING, SUBSTRING)`

  Whether `SUBSTRING` occurs in `STRING`.

* `STRING_LENGTH(STRING)`

  The length of `STRING`.

* `REPEAT(STRING, N)`

  A string consisting of `STRING` repeated `N` times.

### `math`

The `math` extension exposes the following constants and functions, which can be helpful in activities involving math problems.

* `PI`

  An approximation of *π*.

* `TO_DEGREES(X)`

  Converts `X` radians to degrees.

* `TO_RADIANS(X)`

  Converts `X` degrees to radians.

* `SIN(X)`, `COS(X)` & `TAN(X)`

  The sine, cosine and tangent respectively of `X`.

* `ARCSIN(X)`, `ARCCOS(X)` & `ARCTAN(X)`

  The arcsine, arccosine and arctangent respectively of `X`.

* `E`

  An approximation of *e*.

* `LOG(X)`

  The base 10 logarithm of `X`.

* `LN(X)`

  The base *e* logarithm of `X`.

* `LOG(X, B)`

  The base `B` logarithm of `X`.

* `EXP(X)`

  The exponential of `X`.

* `POWER(X, P)`

  `X` raised to the power of `P`.

* `SQUARE(X)`

  The square of `X`.

* `SQUARE_ROOT(X)`

  The square root of `X`.

Example:

`examples/extensions/sine.pseudo`

```text
A = 30
N = 20

loop I from 0 to N - 1
    SPACES = (A * (SIN(I * 2 * PI / N) + 1))
    output REPEAT(" ", SPACES), "*"
end loop
```

From the command line:

```text
python -m ibdp_classes -ext 'strings math' examples/extensions/sine.pseudo 
```

Output:

```text
                               *
                                        *
                                                *
                                                       *
                                                           *
                                                             *
                                                           *
                                                       *
                                                *
                                        *
                               *
                     *
             *
      *
  *
 *
  *
      *
             *
                     *
```

### `bits`

The `bits` extension exposes the following functions, which can be helpful in activities involving bit manipulation.

* `SET_BIT(X, P)`

  Integer `X` with bit at position `P` set.

* `UNSET_BIT(X, P)`

  Integer `X` with bit at position `P` unset.

* `BIT_IS_SET(X, P)`

  Whether the bit at position `P` of integer `X` is set.

* `BIT_AND(A, B)`, `BIT_OR(A, B)`, `BIT_XOR(A, B)`
  
  Bitwise conjunction, disjunction and exclusive disjunction respectively of integers `A` and `B`.

* `BIT_NOT_8(X)`, `BIT_NOT_16(X)` and `BIT_NOT_32(X)`

  Bitwise negation of integer `X` assuming 8, 16 or 32 bits respectively in the structure

Example:

`examples/extensions/binary.pseudo`

```text
TEMPLATE = "[7][6][5][4][3][2][1][0]"

output "Input an integer from 0 to 255."

input VALUE as int

loop I from 0 to 7
    BIT_TEMPLATE = REPLACE("[I]", "I", I)
    if BIT_IS_SET(VALUE, I) then
       TEMPLATE = REPLACE(TEMPLATE, BIT_TEMPLATE, 1)
    else
       TEMPLATE = REPLACE(TEMPLATE, BIT_TEMPLATE, 0)
    end if
end loop

output "In binary,", VALUE, "is:", TEMPLATE
```

In the command line:

```text
python -m ibdp_classes -ext 'strings bits' examples/extensions/binary.pseudo
```

Example output:

```text
Input an integer from 0 to 255.
42
In binary, 42 is: 00101010
```

### `turtle`

The `turtle` extension exposes some of the functionality of the Python turtle module, which can be helpful in fun, beginner-friendly (and more advanced) programming activities. See `src/extensions/turtle_defs.py` for details.

Example:

`examples/extensions/fractal.pseudo`

```text
procedure FRACTAL(LENGTH, DEPTH)
    DISTANCE = LENGTH / 3
    if DEPTH = 0 then
        GO_FORWARD(DISTANCE)
        TURN_LEFT(60)
        GO_FORWARD(DISTANCE)
        TURN_RIGHT(120)
        GO_FORWARD(DISTANCE)
        TURN_LEFT(60)
        GO_FORWARD(DISTANCE)
    else
        FRACTAL(DISTANCE, DEPTH - 1)
        TURN_LEFT(60)
        FRACTAL(DISTANCE, DEPTH - 1)
        TURN_RIGHT(120)
        FRACTAL(DISTANCE, DEPTH - 1)
        TURN_LEFT(60)
        FRACTAL(DISTANCE, DEPTH - 1)
    end if
end procedure

WIDTH = 600
Y = -250

loop DEPTH from 1 to 3
   PEN_UP()
   SET_X(-WIDTH / 2)
   SET_Y(Y)
   PEN_DOWN()
   FRACTAL(WIDTH, DEPTH)
   Y = Y + 200
end loop

HIDE_TURTLE()
WAIT()
```

At the command line:

```text
python -m ibdp_classes -ext turtle examples/extensions/fractal.pseudo  
```

Output:

![See screenshots/turtle.png](screenshots/turtle.png)

## Using the classes within Python scripts

The classed defined by IB can be used directly in Python scripts. While there is not much of a use case for this, it might be helpful as an intermediate step in actually implementing pseudocode.

For example:

```python
from ibdp_classes import Array

def contains(needle: int, haystack: Array[int], n: int) -> bool:
    found = False
    for k in range(n):
        if haystack[k] == needle:
            print("Found!")
            found = True
    return found

haystack = Array(20, -3, 5, 7, 2, 13, 12, 19)
print("haystack:", haystack)

print("5 is in haystack?")
print(contains(5, haystack, 8))

print("4 is in haystack?")
print(contains(4, haystack, 8))
```