# 程序代写代做代考 interpreter Title

Title

Turtle Graphics

1. Week 12+ : Final Assignment

1.1 Turtle Graphics

History

• Many attempts have been made to create programming languages which are intuitive and
easy to learn.

• One of the best of these was LOGO which allowed children as young as 3 to learn a
computer language.

• A subset of this language involved a “turtle” which could be driven around the screen
using simple instructions. The turtle, when viewed from above, was represented by a
triangle.

An Example

{
FD 30
LT 45
FD 30
LT 45
FD 30
LT 45
FD 30
LT 45
FD 30
LT 45
FD 30
LT 45
FD 30
LT 45
FD 30
LT 45

}

2 Chapter 1. Week 12+ : Final Assignment

{
DO A FROM 1 TO 8 {

FD 30
LT 45

}
}

The Formal Grammar

::= “{”
::= |

“}”
::= |

|
|
|

::= “FD”
::= “LT”
::= “RT”
::= “DO” “FROM” “TO”

“{”
::= [A�Z]
::= number |
::= “SET” “:=”
::= | | “;”
::= “+” | “�” | “*” | “/”

Using Variables

{
DO A FROM 1 TO 100 {

SET C := A 1.5 * ;
FD C
RT 62

}
}

1.1 Turtle Graphics 3

Nested Loops

{
DO A FROM 1 TO 50 {

FD A
RT 30
DO B FROM 1 TO 8 {

SET C := A 5 / ;
FD C
RT 45

}
}

}

4 Chapter 1. Week 12+ : Final Assignment

Exercise 1.1 Implement a recursive descent parser – this will report whether or not a given
turtle program follows the formal grammar or not. The input file is specified via argv[1] –
there is no output if the input file is valid. ⌅

25%

Exercise 1.2 Extend the parser, so it becomes an interpreter. The instructions are now
‘executed’. Do not write a new program for this, simply extend your existing parser. Output
is via SDL. ⌅

25%

Exercise 1.3 Show a testing strategy on the above – you should give details of unit testing,
white/black-box testing done on your code. Describe any test-harnesses used. In addition,
give examples of the output of many different turtle programs. Convince me that every line
of your C code has been tested. ⌅

25%

Exercise 1.4 Show an extension to the project in a direction of your choice. It should
demonstrate your understanding of some aspect of programming or S/W engineering. If
you extend the formal grammar make sure that you show the new, full grammar. ⌅

25%

1.1 Turtle Graphics 5

Hints
• Don’t try to write the entire program in one go. Try a cut down version of the grammar

first, e.g.:

::= “{”
::= |

“}”
::= | |
::= “FD”
::= “LT”
::= “RT”
::= number

• The language is simply a sequence of words (even the semi-colons), so use fscanf().
• Some issues, such as what happens if you use an undefined variable, or if you use a variable

before it is set, are not explained by the formal grammar. Use your own common-sense,
and explain what you have done.

• I’m happy to sort extra help sessions in January – ask.
• Please also fill out a hard-copy of the self-assessment questionnaire on the web, so that

you (and I!) have an idea of what mark you expect. Leave this in my room around deadline
day. Don’t forget to fill out your name (you’d be surprised at the number of people who do
….)

Submission
Please create a directory structure, so that I can easily find the different subsections. Your testing
strategy will be explained in testing.txt, and your extension as extension.txt. For the
parser, interpreter and extension sections, make sure there’s a Makefile, so that I can easily
build the code.

—–Top Directory—–

/ | |

/ | |

/ | |

/ | |

parser interp testing extension

| | | |

… … … extension.txt

… … … …

Makefile Makefile … …

testing.txt

Bundle all of these up as one single .zip submission – not one for each subsection.

Week 12+ : Final Assignment
Turtle Graphics

Posted in Uncategorized