/Boaz-Tokenizer-and-Parser

lexical analyser and recursive-descent parser for a high-level language called Boaz, including limited semantic analysis

Primary LanguagePython

Boaz-Tokenizer-and-Parser

Description

My final assignment for my 'Computer Systems' module. The purpose of this assignment was to write a lexical analyser and recursive-descent parser for a high-level language called Boaz, including limited semantic analysis. The program outputs 'ok' if the parsing is a success and 'error' if any issues are encountered, with no error recovery.

How It Works

(Taken from the brief)

Definitions of terminal symbols - lexical analysis:

  • The following are all keywords of the language: begin, char, do, else, end, fi, if, int, od, print, program, then, while. They are case-sensitive and must be all lower-case in the source. These are represented in the grammar by upper-case versions.
  • All symbols within a pair of single quote characters in the grammar are onecharacter or two-character literals that will be found in the source code; e.g. , '!='.
  • IDENTIFIER: A sequence of one or more alphabetic, digit or underscore characters, of which the first must be alphabetic. E.g., Ng1_f3 is valid but 1e4 is not. It is not permitted to define a variable that is the same as a keyword.
  • INT_CONST: A sequence of one or more digits (0-9).
  • CHAR_CONST: A single character enclosed within a pair of double-quote characters. E.g., "!", "a", etc. Multi-character character constants are not permitted.

Limited type checking:

  • If the expression contains at least one relationalOp, booleanOp or unary boolean negation operator (!) then its type is boolean.
  • If the expression is not boolean and it contains at least one CHAR_CONST or an IDENTIFIER of type CHAR then its type is char.
  • If the expression is neither boolean nor char then its type is int.

The following results in a failed parse:

  • Use of an IDENTIFIER either on the left-hand side of an assignStatement or in a term that has not been declared within a varDec.
  • Assignment of an expression of one type to a variable of a different type in an assignStatement. It is only legal to assign a char expression to a variable of type char, and an int expression to a variable of type int. It is not permitted to assign a boolean expression to any variable.
  • Use of an expression of type int or char in the expression (condition) of either an ifStatement or whileStatement. All condition expressions must be of type boolean.

Process