Little Quilt

Original Little Quilt

Little Quilt is a very small language for designing quilts. It is based on ML syntax. The language definition can be found in the book Programming Languages: Concepts and Constructs. Ravi Sethi. Addison-Wesley, 1996. Scanned versions of the relevant pages are provided through internal links and are meant purely for academic use: page 1, page 2, page 3, page 4, page 5, page 6, page 7, page 8.

Please do not try to print the pages. If you need a hard copy, take one from me and make as many xeroxes as you like.

(An Indian edition of the book is available locally and is strongly recommended if you are interested in understanding different programming paradigms.)

Enhancements in Little Quilt

The original Little Quilt does not support assignment statements, conditionals, iterative construct, or self-recursion. For the purpose of CS394, they have to be supported.

Now comments can be included in quilt programs. They begin with a % character and end with a new line (or end of file) character.
A quilt expression can be
- One of the usual quilt expressions defined in the Original Little Quilt.
- A special empty quilt EQ.
- A quilt obtained by the head and tail operations.
  These operations view a quilt as rectangular matrix where each element can be one of the following
  - a0, b0 : quilt a or b.
  - a1, b1 : quilt a or b turned 90 degrees clockwise.
  - a2, b2 : quilt a or b turned 180 degrees clockwise.
  - a3, b3 : quilt a or b turned 270 degrees clockwise.
  The actual operations are
  - hdRow(q) : compute the quilt represented by the first row of the matrix corresponding to quilt q.
  - tlRow(q) : compute the quilt represented by the rows remaining after removing the first row of the matrix corresponding to quilt q.
  - hdCol(q) : compute the quilt represented by the the first column of the matrix corresponding to quilt q.
  - tlCol(q) : compute the quilt represented by the columns remaining after removing the first column of the matrix corresponding to quilt q.
- A sequence of statements ending in a result statement. The value of the expression is the quilt appearing in the result statement.
Each statement is terminated by a semi-colon and can be one of the following kind
- Assignment Statement.
  Variable = QuiltExpression ;
  The left hand side is an undeclared variable representing a quilt. The right hand side is a quilt expression.
- Conditional Statement.
  if (QuiltExpression RelOp QuiltExpression) then StatementList fi ;
  The relational operator can be test of equality ( == ) or test of inequalty ( != ). An alternative version of the conditional statement is
  if (QuiltExpression RelOp QuiltExpression) then StatementList else StatementList fi ;
- Looping Statement.
  while (QuiltExpression RelOp QuiltExpression) do StatementList od ;
- Result Statement.
  result QuiltExpression ;

Examples of Valid Programs

This is my first program nq0 in the New Quilt.
Some programs in original quilt, which are also valid programs in New quilt are
- q0, matrix version, and its picture.
- q1, matrix version, and its picture.
- q2, matrix version, and its picture.
- q3, matrix version, and its picture.
- q4, matrix version, and its picture.
- q5, matrix version, and its picture.
- q6, matrix version, and its picture.
- q7, matrix version, and its picture.
- q12, matrix version, and its picture.
The following programs are syntactically valid but semantically invalid : q8, q9, q10, and q11.
Here is the binary executable of a reference implementation of a parser for the New Quilt. Semantic checks have not been inserted in this implementation and it is a pure parser which checks only for syntax and quits with a terse "syntax error" if the input is not valid syntactically.
This has been compiled on a Fedora Core 1 running on P4. I expect it to work on common versions of Linux running on a pentium processor.