Cambridge Pseudocode Interpreter

A fully-featured interpreter for the Cambridge International AS & A Level Computer Science (9618) pseudocode language.

Overview

This project implements an interpreter for the pseudocode specification used in Cambridge International AS & A Level Computer Science examinations. It supports all major language features including:

• Variables and constants
• All primitive data types (INTEGER, REAL, STRING, CHAR, BOOLEAN, DATE)
• Arrays (1D and 2D)
• Records (composite data types)
• Selection (IF/THEN/ELSE, CASE)
• Iteration (FOR, WHILE, REPEAT)
• Procedures and functions
• Parameter passing (BYVAL, BYREF)
• File handling
• Object-oriented programming (classes, inheritance)
• Built-in functions

Installation

🍺 Homebrew

brew tap andrinoff/cambridge
brew install cambridge
brew install cambridge-lsp # Optinal, Language Server Protocol

Snapcraft

snap install cambridge

Already built binaries

I build all binaries, and they are available here

Build From Source

git clone https://github.com/andrinoff/cambridge-lang.git
cd cambridge-lang
go build -o cambridge ./cmd/cambridge

Usage

# Run a pseudocode file
./cambridge run program.pseudo

# Start interactive REPL
./cambridge repl

# Show version
./cambridge version

# Show help
./cambridge help

Language Reference

Variables and Constants

DECLARE Name : STRING
DECLARE Age : INTEGER
DECLARE Height : REAL
DECLARE IsStudent : BOOLEAN

CONSTANT PI = 3.14159
CONSTANT GREETING = "Hello"

Name <- "Alice"
Age <- 17

Data Types

Type	Description	Example
INTEGER	Whole numbers	42, -17
REAL	Floating-point numbers	3.14, -0.5
STRING	Text strings	"Hello"
CHAR	Single character	'A'
BOOLEAN	True/False	TRUE, FALSE
DATE	Date values	-

Arrays

// 1D Array
DECLARE Numbers : ARRAY[1:10] OF INTEGER
Numbers[1] <- 100

// 2D Array
DECLARE Matrix : ARRAY[1:3, 1:3] OF INTEGER
Matrix[1, 2] <- 5

Selection

// IF statement
IF Score >= 90 THEN
    Grade <- "A"
ELSE
    Grade <- "B"
ENDIF

// CASE statement
CASE OF DayNumber
    1 : OUTPUT "Monday"
    2 : OUTPUT "Tuesday"
    6, 7 : OUTPUT "Weekend"
    OTHERWISE : OUTPUT "Midweek"
ENDCASE

Iteration

// FOR loop
FOR i <- 1 TO 10
    OUTPUT i
NEXT i

// FOR with STEP
FOR i <- 10 TO 0 STEP -2
    OUTPUT i
NEXT i

// WHILE loop
WHILE Count < 10
    Count <- Count + 1
ENDWHILE

// REPEAT loop
REPEAT
    INPUT Value
UNTIL Value > 0

Procedures and Functions

// Procedure
PROCEDURE Greet(Name : STRING)
    OUTPUT "Hello, ", Name
ENDPROCEDURE

CALL Greet("World")

// Function
FUNCTION Square(N : INTEGER) RETURNS INTEGER
    RETURN N * N
ENDFUNCTION

Result <- Square(5)

// BYREF parameter
PROCEDURE Swap(BYREF A : INTEGER, BYREF B : INTEGER)
    DECLARE Temp : INTEGER
    Temp <- A
    A <- B
    B <- Temp
ENDPROCEDURE

Records

TYPE Student
    DECLARE Name : STRING
    DECLARE Age : INTEGER
    DECLARE Grade : CHAR
ENDTYPE

DECLARE MyStudent : Student
MyStudent.Name <- "Alice"
MyStudent.Age <- 17

File Handling

// Writing to a file
OPENFILE "data.txt" FOR WRITE
WRITEFILE "data.txt", "Hello, World!"
CLOSEFILE "data.txt"

// Reading from a file
OPENFILE "data.txt" FOR READ
WHILE NOT EOF("data.txt")
    READFILE "data.txt", Line
    OUTPUT Line
ENDWHILE
CLOSEFILE "data.txt"

// Appending to a file
OPENFILE "data.txt" FOR APPEND
WRITEFILE "data.txt", "New line"
CLOSEFILE "data.txt"

Object-Oriented Programming

CLASS Animal
    PRIVATE Name : STRING
    
    PUBLIC PROCEDURE NEW(GivenName : STRING)
        Name <- GivenName
    ENDPROCEDURE
    
    PUBLIC FUNCTION GetName() RETURNS STRING
        RETURN Name
    ENDFUNCTION
ENDCLASS

CLASS Dog INHERITS Animal
    PUBLIC PROCEDURE Speak()
        OUTPUT GetName(), " says Woof!"
    ENDPROCEDURE
ENDCLASS

DECLARE MyDog : Dog
MyDog <- NEW Dog("Buddy")
CALL MyDog.Speak()

Built-in Functions

String Functions

Function	Description	Example
LENGTH(s)	Returns string length	LENGTH("Hello") → 5
LEFT(s, n)	Returns leftmost n characters	LEFT("Hello", 2) → "He"
RIGHT(s, n)	Returns rightmost n characters	RIGHT("Hello", 2) → "lo"
MID(s, start, len)	Returns substring	MID("Hello", 2, 3) → "ell"
UCASE(c)	Converts to uppercase	UCASE('a') → 'A'
LCASE(c)	Converts to lowercase	LCASE('A') → 'a'

Character/ASCII Functions

Function	Description	Example
ASC(c)	Returns ASCII value	ASC('A') → 65
CHR(n)	Returns character for ASCII value	CHR(65) → 'A'

Numeric Functions

Function	Description	Example
INT(x)	Returns integer part	INT(3.7) → 3
RAND(n)	Random real 0 to n	RAND(10) → 7.23
ROUND(x, p)	Rounds to p decimal places	ROUND(3.456, 2) → 3.46
ABS(n)	Absolute value	ABS(-5) → 5
SQRT(n)	Square root	SQRT(16) → 4
POW(b, e)	Power (b^e)	POW(2, 3) → 8

Conversion Functions

Function	Description	Example
NUM_TO_STR(n)	Number to string	NUM_TO_STR(42) → "42"
STR_TO_NUM(s)	String to number	STR_TO_NUM("42") → 42

File Functions

Function	Description
EOF(filename)	Returns TRUE if at end of file

Operators

Arithmetic

Operator	Description
+	Addition
-	Subtraction
*	Multiplication
/	Division (returns REAL)
DIV	Integer division
MOD	Modulus (remainder)

Comparison

Operator	Description
=	Equal to
<>	Not equal to
<	Less than
>	Greater than
<=	Less than or equal
>=	Greater than or equal

Logical

Operator	Description
AND	Logical AND
OR	Logical OR
NOT	Logical NOT

String

Operator	Description
&	Concatenation

Examples

See the examples/ directory for complete example programs:

• hello.pseudo - Hello World
• variables.pseudo - Variables and constants
• selection.pseudo - IF and CASE statements
• loops.pseudo - FOR, WHILE, REPEAT loops
• functions.pseudo - Procedures and functions
• arrays.pseudo - Array operations
• strings.pseudo - String manipulation
• records.pseudo - Record types
• oop.pseudo - Object-oriented programming
• fileio.pseudo - File handling

Specification

This interpreter is based on the Cambridge International AS & A Level Computer Science (9618) pseudocode specification. For the official specification, see:

• Cambridge 9618 Pseudocode Guide for Teachers (2026)

License

MIT License