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>
BackParser	The parser for the BACK instruction.
CharTokenParser
CleanParser
ClearScreenParser
DifferenceParser
EqualParser
ForwardParser	The parser for the forward instruction
GreaterParser
HeadingParser
HideTurtleParser	The parser for the HIDETURTLE instruction
HomeParser	The 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
LeftParser	The parser for the LEFT instruction.
LessParser
MinusParser
NotEqualParser
PenDownParser
PenDownPParser
PenUpParser
PrintParser	The parser for the print instruction
QuotientParser
RemainderParser
RepeatParser	Parse a REPEAT Statement, which looks like REPEAT numOrVar [ instructionlist ]
RightParser	The parser for the RIGHT instruction.
SetXParser
SetXYParser	The parser for the SETXY instruction
SetYParser
ShowTurtleParser	The parser for the SHOWTURTLE instruction
StrictInstructionListParser	The parser for lists of instructions.
SumParser
TowardsParser
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.