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>
BackwardParser	Parse a BACKWARD Statement, which looks like BACKWARD dist
BKParser	Parse a BACKWARD Statement, which looks like BACKWARD dist
CleanParser	Parse a CLEAN Statement, which looks like CLEAN
ClearScreenParser	Parse a CLEARSCREEN Statement, which looks like CLEARSCREEN
CSParser	Parse a CS Statement, which looks like CS
DifferenceParser	Parse a DIFFERENCE Statement, which looks like DIFFERENCE num1 num2
FDParser	Parse a FORWARD Statement, which looks like FORWARD dist
ForwardParser	Parse a FORWARD Statement, which looks like FORWARD dist
HeadingParser	Parse an Heading Statement, which looks like HEADING
HideTurtleParser	Parse a HIDETURTLE Statement, which looks like HIDETURTLE
HomeParser	Parse a Home Statement, which looks like Home
HTParser	Parse a HT Statement, which looks like HT
IdentifierParser	Parse an assignment statement, which looks like <id> <assignment_token, i.e., = > <expression>
IfParser	Parse an IF Statement, which looks like IF varOrCommand [ instructionlist ]
InstructionNames	Reads the file of instruction names.
InstructionParser	Instruction Parser - calls appropriate Parser for each Instruction
IsEqualParser	Parse an IsEqual Statement, which looks like EQUAL num1 num2
IsGreaterParser	Parse an ISGREATER Statement, which looks like ISGREATER num1 num2
IsLessParser	Parse an IsLess Statement, which looks like ISLESS num1 num2
IsNotEqualParser	Parse an IsNotEqual Statement, which looks like NOTEQUAL num1 num2
LeftParser	Parse a Left Statement, which looks like Left dist
LTParser	Parse a Left Statement, which looks like Left dist
MinusParser	Parse a MINUS Statement, which looks like MINUS num
PenDownParser	Parse a PENDOWN Statement, which looks like PENDOWN
PenDownPParser	Parse a PENDOWNP Statement, which looks like PENDOWNP
PenUpParser	Parse a PENUP Statement, which looks like PENUP
PrintParser	The parser for the print instruction
ProductParser	Parse a PRODUCT Statement, which looks like PRODUCT num1 num2
QuotientParser	Parse a QUOTIENT Statement, which looks like QUOTIENT num1 num2
RemainderParser	Parse a REMAINDER Statement, which looks like REMAINDER num1 num2
RepeatParser	Parse a REPEAT Statement, which looks like REPEAT numOrVar [ instructionlist ]
RightParser	Parse a RIGHT Statement, which looks like RIGHT dist
RTParser	Parse a RIGHT Statement, which looks like RIGHT dist
SetxParser	Parse a Setx Statement, which looks like Towards xcor
SetxyParser	Parse a Setxy Statement, which looks like Towards xcor ycor
SetyParser	Parse a Sety Statement, which looks like Towards ycor
ShowTurtleParser	Parse a SHOWTURTLE Statement, which looks like SHOWTURTLE
STParser	Parse a ST Statement, which looks like ST
StrictInstructionListParser	The parser for lists of instructions.
SumParser	Parse a SUM Statement, which looks like SUM num1 num2
TokenNames	Reads the file of instruction names.
ToParser	Parse a TO Statement, which looks like TO sub_name [ instructionlist ]
TowardsParser	Parse a Towards Statement, which looks like Towards xcor ycor
XCorParser	Parse an XCor Statement, which looks like XCOR
YCorParser	Parse an YCor Statement, which looks like YCOR

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.