Little Quilt Compiler Implementation in PLY
Little Quilt is a small language introduced by Ravi Sethi in his book ‘Programming Languages’. Here, a restricted version of Little Quilt is presented.
The language is defined by the following BNF grammar:
<QUILT> ::= A | B | turn(<QUILT>) | sew(<QUILT>,<QUILT>)
A and B represent the two primitive quilts. Each primitive quilt corresponds to a matricial arrangement of 2 × 2 characters. turn() and sew() are operations over quilts.
The instruction turn(x) turns the quilt x 90 degrees clockwise. The following table illustrates the primitive quilts as well as examples of the effect of the turn() operation:
Accordingly, the instruction sew(x,y) sews quilt x to the left of quilt y. Both x and y must have the same height, otherwise an error will be generated. The following figure represents the result of sew(A,turn(B)):
while the sew(turn(sew(B,turn(B))),A) generates an error message.