Plang Specification

Extension:

.plg

Token Rules

# Plang File Example

VAR file

WHILE file IS NOT empty
    DO PrintLine

  • Comments are single line

    • Start with #
    • Entire line becomes comment

  • Variables are initiated with VAR keyword

    • Must be first token on line
      • Allowed: VAR myVar = 55
      • Not Allowed: IF file IS NOT empty VAR myVar = 55
    • VAR must be followed by 'WORD' token, which will be the variable name
      • Does require space before word
        • Allowed: VAR myVar
        • Not Allowed: VARmyVar
    • 'WORD' can optionally be followed by =
      • Required to have spaces on both sides
      • Must be followed by either a 'WORD' or a 'NUMBER'

Lexer Logic

Character Categories
Category Characters
ALPHA a-z, A-Z
DIGIT 0-9
OPERATOR +, -, *, /, <, >, =, !
SPACE , \n, \r, \t
COMMENT_INDICATOR #
State flow

The state is the state the system is currently in. If the current scanned char is in the state terminator category, the tokens are made accordingly, and the machine is set into the target state.

In the case of the terminator being an OPERATOR, the next character may be checked to determine the correct token, such as in the event of += or <=. The currentIndex will be incremented one extra unit to compensate for this additional token char, as to skip the next char from the scan.

State State Terminator Target State
Normal ALPHA Word
Normal DIGIT Number
Normal COMMENT_INDICATOR Comment
Normal SPACE -
Word SPACE Normal
Word COMMENT_INDICATOR Comment
Word OPERATOR Normal
Number SPACE Normal
Number COMMENT_INDICATOR Comment
Number OPERATOR Normal
Comment SPACE_END_OF_LINE Normal

Parser

Context Free Grammar
Name Rule
START VAR_DEC
VAR_DEC word word = VALUE
VALUE word / number