Lab 5: Scanning & Parsing
Bard College – Computer Science – Design of Programming Languages

This labs gives us practice using the lexing and parsing tools to interpret (non-lisp) programs. Specifically, we’ll be processing JavaScript Object Notation (JSON). 

From Eloquent JavaScript: “JSON is widely used as a data storage and communication format on the Web, even in languages other than JavaScript.” 

Fun data sets represented in JSON can be found in Darius Kazemi’s  corpora project.

We will be using Racket for this lab; more on strings in Racket.

Warm Up: Infix Expressions

Use sllgen  and define-datatype to parse infix expressions (from Exercise B.1). 
#lang racket
(require eopl)

(define the-lexical-spec
  '((whitespace (whitespace) skip)
    (mul-op ("*") symbol)
    (add-op ("+") symbol)
    (number (digit (arbno digit)) number)))

(define the-grammar
  '((a-expr ;:==
        (a-term (arbno add-op a-term))       binop)
    (a-term ;:==
        (a-factor (arbno mul-op a-factor))   binop)
    (a-factor ;:==
         (number)                            number)
    (a-factor ;:==
         ("(" a-expr ")")                    factor)))

(define-datatype infix infix?
    (left infix?)
    (operators (list-of symbol?))
    (right (list-of infix?)))
    (value infix?))
    (value integer?)))

(define just-scan
    (sllgen:make-string-scanner the-lexical-spec the-grammar))

(define scan&parse
  (sllgen:make-string-parser the-lexical-spec the-grammar))