Package elan.parser

This package is responsible for parsing the language Elan.

See:
Description

Interface Summary

Parser

Class Summary

AddParser
AndParser
AssignmentParser
BackgroundParser
BackParser
BgParser
BkParser
CleanParser
ClearscreenParser
CsParser
DifferenceParser
ElanParser	Illustrates the java.io.StreamTokenizer class and how it can be used to parse tokens for a toy example programming language (elan) For this example simple instructions are parsed, but lots of infrastructure is in place for parsing a more complete language.
EqualboolParser
ExpressionParser	This is a recursive descent parser for parsing expressions using the standard grammar for expressions (follows).
FdParser
FenceParser
ForwardParser
GreaterParser
HeadingParser
HideturtleParser
HomeParser
HtParser
IdentifierParser
IfParser
InstructionNames
InstructionParser	InstructionParser parses instructions; it uses token types to call appropriate parsers, and throws ParseExceptions in cases of error.
LeftParser
LessParser
LtParser
MinusParser
NotequalParser
NotParser
OrParser
PcParser
PdParser
PencolorParser
PendownParser
PendownpParser
PendownqParser
PensizeParser
PenupParser
PrintParser
ProductParser
PsParser
PuParser
QuotientParser
RandomnumParser
RemainderParser
RepeatParser
RightParser
RtParser
SetbackgroundParser
SetbgParser
SetheadingParser
SethParser
SetpaletteParser
SetpcParser
SetpencolorParser
SetpensizeParser
SetpsParser
SetshapeParser
SetshParser
SetxParser
SetxyParser
SetyParser
ShapeParser
ShowturtleParser
StParser
StrictInstructionListParser	The StrictInstructionListParser parses a StrictInstructionList in the case of user-defined functions/
SumParser
TellParser
ToParser
TowardsParser
WindowParser
WrapParser
XcorParser
YcorParser

Exception Summary

FunctionArgumentException
FunctionNameException
ParseException

Package elan.parser Description

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

Adding/Parsing a New Instruction

To parse a new instruction the following steps are followed. In the exposition 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 elan.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.

Owen L. Astrachan

Last modified: Wed Nov 28 13:22:28 EST 2001