Package slogo.parser

This package is responsible for parsing the language SLogo.

See: Description

Interface Summary

Interface	Description
Parser	The interface that all parsers must implement

Class Summary

Class	Description
AssignmentParser	Parse an assignment statement, which looks like <id> <assignment_token, i.e., = > <expression>
ExpressionParser	This is a recursive descent parser for parsing expressions using the standard grammar for expressions (follows).
FDParser	Parse a FORWARD Statement, which looks like FORWARD numOrVar [ instructionlist ]
ForwardParser	Parse a FORWARD Statement, which looks like FORWARD numOrVar [ instructionlist ]
IdentifierParser	Parser for identifiers
InstructionChecker
InstructionNames	Reads the file of instruction names.
InstructionParser	Instruction Parser - calls appropriate Parser for each Instruction
PrintParser	The parser for the print instruction
RepeatParser	Parse a REPEAT Statement, which looks like REPEAT numOrVar [ instructionlist ]
RightParser	Parse a RIGHT Statement, which looks like RIGHT numOrVar
SLogoParser	Illustrates the java.io.StreamTokenizer class and how it can be used to parse tokens for a subset of the SLogo programming language.
StrictInstructionListParser	The parser for lists of instructions.

Exception Summary

Exception	Description
ParseException	A specialized exception class for parsing errors

Package slogo.parser Description

This package is responsible for parsing the language SLogo. It uses recursive descent with, currently, no lookahead.

Adding/Parsing a New Instruction

To parse a new instruction the following steps are followed. We'll use the addition of a statement for an If instruction to the language as an example.

1. Create a token for the instruction (probably a subclass of token.ReservedToken) with the same prefix as the new instruction, e.g., IfToken.java.
2. Create a parser for the instruction with the same prefix as the instruction, e.g., IfParser.java. The parsing class (presumably implementing Parser) will return an instance of the parsed Instruction, see the next item.
3. Create an instruction with prefix name, e.g., If.java in the slogo.instruction package.
4. Add the instruction name to the file instructions.prop, e.g., add a single line to the file containing the string If.