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Thank you very much, Prof.Wand.These days, I meet two other questions.1. In page 60 of EOPL3, figure 3.2, one can seeExpression ::= -(Expression , Expression)diff-exp (exp1 exp2)here, what does "-" mean? it seems do not like substraction.
2. In the page 60,(scan&parse "-(55, -(x,11))")#(struct:a-program#(struct:diff-exp#(struct:const-exp 55)#(struct:diff-exp#(struct:var-exp x)#(struct:const-exp 11))))Here, what does "scan&parse" mean ? In racket, I do not find its defintion.