PLC Semester Project

This course will discuss how programming languages are constructed and analyze the methodology used to create existing languages. Topics included are: lexical analysis, scanning, programmatic semantics, code generation, and different types of programming languages.

Part 1: Lexer

The lexer works through three main functions:

• lex(), which repeatedly calls lexToken() and skips whitespace
• lexToken(), which lexes the next token
• CharStream, which manages the state of the lexer and literals

If the lexer fails to parse something (such as an unterminated string) a ParseException is thrown with an index at the character which is invalid.

Part 2: Parser

The parser takes the sequence of tokens emitted by the lexer and turns that into a structured representation of the program, called the Abstract Syntax Tree (AST).

Part 3: Interpreter

Part 4: Analyzer

Part 5: Generator

Parser Grammar

source ::= global* function*

global ::= ( list | mutable | immutable ) ';' list ::= 'LIST' identifier '=' '[' expression (',' expression)* ']' mutable ::= 'VAR' identifier ('=' expression)? immutable ::= 'VAL' identifier '=' expression

function ::= 'FUN' identifier '(' (identifier (',' identifier)* )? ')' 'DO' block 'END'

block ::= statement*

statement ::= 'LET' identifier ('=' expression)? ';' | 'SWITCH' expression ('CASE' expression ':' block)* 'DEFAULT' block 'END' | 'IF' expression 'DO' block ('ELSE' block)? 'END' | 'WHILE' expression 'DO' block 'END' | 'RETURN' expression ';' | expression ('=' expression)? ';'

expression ::= logical_expression

logical_expression ::= comparison_expression (('&&' | '||') comparison_expression)* comparison_expression ::= additive_expression (('<' | '>' | '==' | '!=') additive_expression)* additive_expression ::= multiplicative_expression (('+' | '-') multiplicative_expression)* multiplicative_expression ::= primary_expression (('' | '/' | '^') primary_expression)

primary_expression ::= 'NIL' | 'TRUE' | 'FALSE' | integer | decimal | character | string | '(' expression ')' | identifier ('(' (expression (',' expression)*)? ')')? | identifier '[' expression ']'

identifier ::= '@'? [A-Za-z] [A-Za-z0-9_-]* integer ::= '0' | '-'? [1-9] [0-9]* decimal ::= '-'? ('0' | [1-9] [0-9]) '.' [0-9]+ character ::= ['] ([^'\n\r\\] | escape) ['] string ::= '"' ([^"\n\r\\] | escape) '"' escape ::= '' [bnrt'"\] operator ::= [!=] '='? | '&&' | '||' | 'any character'

whitespace ::= [ \b\n\r\t]