CFPL-Interpreter

An interpreter for CFPL (CIT-University's First Programming Language)

Language Specification of CIT-University's First Programming Language

Introduction

CFPL is a very simple programming language that allows the programmer to achieve fluency in minutes.
It is a strongly typed programming language. 
It is intended for students enrolled in programming languages.
It aims to train them on how to build a pure interpreter. 

Language Grammar

Program Structure:
1. Every line contains a single statement
2. All variable declaration is found on top of the program
3. A line that starts with asterisk(*) is considered as a comment and comment can be found in any
   part of the program
4. executable code should be found inside the START and STOP block
5. all reserved words are in capital letters
6. sharp sign(#) signifies next line or carriage return
7. ampersand(&) serves as a concatenator
8. the square braces([]) are as escape code

Data Types:
  INT – an ordinary number with no decimal part. It uses 32 bits. It can be positive or negative.
  CHAR – a single symbol. It uses UNICODE.
  BOOL – represents the literals TRUE or FALSE.
  FLOAT – a number with decimal part.  It uses 64 bits.

Operators:
  Arithmetic operators
    ( )         - parenthesis
    *, /, %     - multiplication, division, modulo
    +, -        - addition, subtraction
    >, <        - greater than, lesser than
    >=, <=      - greater than or equal to, lesser than or equal to
    ==, <>      - equal, not equal

  Logical operators (<BOOL expression><LogicalOperator><BOOL expression>)
    AND     - needs the two BOOL expression to be true to result to true, else false
    OR      - if one of the BOOL expressions evaluates to true, returns true, else false
    NOT     - the reverse value of the BOOL value

  Unary operator
    +     - positive
    -     - negative

Control structures:
  If-else statement
    IF (<BOOL expression>)
    START
      <statement>
    STOP

    IF (<BOOL expression>)
    START
      <statement>
    STOP

    ELSE
    START
      <statement>
    STOP

  While statement
  WHILE (<BOOL expression>)
    START
      <statement>
    STOP


INPUT – allow the user to input a value to a data type.
Syntax:
  INPUT: <variableName>[,<variableName>]*
Sample use:
  INPUT: x, y
means in the screen you have to input two values separated by comma(,)

Sample Programs

Program 1

* my first program in CFPL
VAR abc, b, c AS INT
VAR x, w_23='w' AS CHAR
VAR t="TRUE" AS BOOL
START
  abc=b=10
  w_23='a'
  * this is a comment
  OUTPUT: abc & "hi" & b & "#" & w_23 & "[#]"
STOP

Output 1

10hi10
a#

Program 2

VAR xyz, abc=100 AS INT
START
  xyz= ((abc *5)/10 + 10) * -1
  * xyz should have the value -60
  OUTPUT: "[[]" & xyz & "[]]"
STOP

Output 2

[-60]

Program 3

VAR a=100, b=200, c=300 AS INT
VAR d="FALSE" AS BOOL
START
  d = (a < b AND c <>200)
  OUTPUT: d
STOP

Output 3

TRUE

Program 4

VAR a=100, b=200, c=300 AS INT
VAR d="FALSE", e="TRUE" AS BOOL
START
  d = (a < b AND c <>200)
  e = NOT d
  IF (d)
  START
    OUTPUT: "IF BLOCK#"
  STOP
  ELSE
  START
    OUTPUT: "ELSE BLOCK#"
  STOP
  IF (c <> 300)
  START
    OUTPUT: "IF BLOCK#"
  STOP
  ELSE
  START
    OUTPUT: "ELSE BLOCK#"
  STOP
STOP

Output 4

IF BLOCK
ELSE BLOCK

Program 5

VAR i=10 AS INT
START
WHILE (i >= 0)
  START
    OUTPUT: i & "#"
    IF (i == 0)
    START
      OUTPUT: "End of loop!"
    STOP
    i = i - 1
  STOP
STOP

Output 5

10
9
8
7
6
5
4
3
2
1
0
End of loop!