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	Parse a BK Statement, which can look like either BACK dist or BK dist
CleanParser	Parse a CLEAN Statement, which simply looks like CLEAN
ClearScreenParser	Parse a CLEARSCREEN Statement, which can look like either CLEARSCREEN or CS
DifferenceParser	Parse a DIFFERENCE Statement, which looks like DIFFERENCE num1 num2
EqualBoolParser	Parse a EQUAL? Statement, which looks like EQUAL? thing1 thing2
ForwardParser	Parse an FD Statement, which can look like either FORWARD dist or FD dist
GreaterParser	Parse an GREATER? Statement, which looks like GREATER? num1 num2
HeadingParser	Parse a HEADING Statement, which simply looks like HEADING
HideTurtleParser	Parse a HT Statement, which can look like either HIDETURTLE or HT
HomeParser	Parse a HOME Statement, which simply looks like HOME
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
LeftParser	Parse a LT Statement, which can look like either LEFT degrees or LT degrees
LessParser	Parse a LESS? statement, which looks like LESS? num1 num2
MinusParser	Parse a MINUS statement, which looks like MINUS num
NotEqualParser	Parse a NOTEQUAL? Statement, which looks like NOTEQUAL? thing1 thing2
PenDownParser	Parse a PENDOWN? Statement, which can look either like PENDOWN or PD
PenDownPParser	Parse a PENDOWNP Statement, which can look like either PENDOWNP or PENDOWN?
PenUpParser	Parse a PENUP Statement, which can look either like PENUP or PU
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	Parses a REMAINDER statement, which looks like REMAINDER num1 num2
RepeatParser	Parse a REPEAT Statement, which looks like REPEAT numOrVar [ instructionlist ]
RightParser	Parse a RT Statement, which can look like either RIGHT degrees or RT degrres
SetXParser	Parses a SETX command, which looks like SETX xcor
SetXYParser	Parses a SETY command, which looks like SETXY xcor ycor
SetYParser	Parses a SETY command, which looks like SETY ycor
ShowTurtleParser	Parses an ST command, which can look like either SHOWTURTLE or ST
StrictInstructionListParser	The parser for lists of instructions.
SumParser	Parses a SUM parser, which looks like SUM num1 num2
ToParser	Parse a TO Statement, which looks like TO sub_name [instructionlist]
TowardsParser	Parses a TOWARDS statement, which looks like TOWARDS xcor ycor
XcorParser	Parse an XCOR Statement, which simply looks like XCOR
YcorParser	Parse a YCOR Statement, which simply 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.