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>
BKParser	Parser for the BK instruction
CleanParser	Parser for the BK instruction
ClearScreenParser	Parser for the ClearScreen instruction
DifferenceParser
EqualsParser	Parser for the Equal instruction
FDParser	Parser for the FD instruction
GreaterParser	Parser for the Greater instruction
HeadingParser
HomeParser	Parser for the Home instruction
IdentifierParser	Parse an assignment statement, which looks like <id> <assignment_token, i.e., = > <expression>
IfParser
InstructionNames	Reads the file of instruction names.
InstructionParser	Instruction Parser - calls appropriate Parser for each Instruction
LessParser	Parser for the Less instruction
LTParser
MinusParser
NotEqualsParser	Parser for the NotEquals instruction
PDParser
PrintParser	The parser for the print instruction
ProductParser
PUParser	Parser for the Pen Up instruction
QuotientParser
RemainderParser
RepeatParser	Parse a REPEAT Statement, which looks like REPEAT numOrVar [ instructionlist ]
RTParser
SetPCParser	Parser for the SetPenColor instruction
SetPSParser	Parser for the SetPenSize instruction
SetXParser	Parser for the SetX instruction
SetXYParser	Parser for the SetXY instruction
SetYParser	Parser for the SetX instruction
StrictInstructionListParser	The parser for lists of instructions.
SubroutineParser	Parse an assignment statement, which looks like <id> <assignment_token, i.e., = > <expression>
SumParser	Parser for the FD instruction
ToParser
TowardsParser	Parser for the SetXY instruction
XCorParser
YCorParser

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 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.