Beau­tiful Racket / racket school 2019

• 1 intro
• 2 taco compiler
• 3 the tacopoca­lypse
• 4 tacogram
• 5 taco victory



#lang tacopocalypse-prep
(() taco () taco () () ())
(() taco () taco () () ())
(() taco () () () taco ())
(() () () taco () taco taco)
(taco () taco () () taco taco)
(() () taco taco () taco taco)
(() () taco taco () taco taco)
(taco taco taco taco () taco taco)
(() () () () () taco ())
(taco taco taco () taco taco taco)
(taco taco taco taco () taco taco)
(() taco () () taco taco taco)
(() () taco taco () taco taco)
(() () taco () () taco taco)
(() taco () () () taco ())
(() taco () taco () () ())
(() () () taco () taco ())
(taco taco () taco () taco ())
(() () () () () taco ())
(taco () () () taco taco ())
(() () () () () taco ())
(() () () taco () taco ())
(() taco () taco () taco ())
(() () () () () taco ())
(() taco () () taco taco ())
(() () () () () taco ())
(() () () taco () taco ())
(taco () taco taco () taco ())
(() () () () () taco ())
(() () () taco taco taco taco)
(taco () () taco () taco ())
(taco () () taco () taco ())
(taco () () taco () taco ())



#lang tacopoca­lypse-prep
(() taco () taco () () ())
(() taco () taco () () ())
(() taco () () () taco ())
(() () () taco () taco taco)
(taco () taco () () taco taco)
(() () taco taco () taco taco)
(() () taco taco () taco taco)
(taco taco taco taco () taco taco)
(() () () () () taco ())
(taco taco taco () taco taco taco)
(taco taco taco taco () taco taco)
(() taco () () taco taco taco)
(() () taco taco () taco taco)
(() () taco () () taco taco)
(() taco () () () taco ())
(() taco () taco () () ())
(() () () taco () taco ())
(taco taco () taco () taco ())
(() () () () () taco ())
(taco () () () taco taco ())
(() () () () () taco ())
(() () () taco () taco ())
(() taco () taco () taco ())
(() () () () () taco ())
(() taco () () taco taco ())
(() () () () () taco ())
(() () () taco () taco ())
(taco () taco taco () taco ())
(() () () () () taco ())
(() () () taco taco taco taco)
(taco () () taco () taco ())
(taco () () taco () taco ())
(taco () () taco () taco ())



##$%#$%#$#$#$$##$%#$%#$#$#$$##$%#$#$#$%#$$##$#$#$%#$%%$#%#$%#$#$%%$##$#$%%#$%%$##$#$%%#$%%$#%%%%#$%%$##$#$#$#$#$%#$$#%%%#$%%%$#%%%%#$%%$##$%#$#$%%%$##$#$%%#$%%$##$#$%#$#$%%$##$%#$#$#$%#$$##$%#$%#$#$#$$##$#$#$%#$%#$$#%%#$%#$%#$$##$#$#$#$#$%#$$#%#$#$#$%%#$$##$#$#$#$#$%#$$##$#$#$%#$%#$$##$%#$%#$%#$$##$#$#$#$#$%#$$##$%#$#$%%#$$##$#$#$#$#$%#$$##$#$#$%#$%#$$#%#$%%#$%#$$##$#$#$#$#$%#$$##$#$#$%%%%$#%#$#$%#$%#$$#%#$#$%#$%#$$#%#$#$%#$%#$$



##$%#$%#$#$#$$##$%#$%#$#$#$$##$%#$#$#$%#$$##$#$#$%#$%%$#%#$%#$#$%%$##$#$%%#$%%$##$#$%%#$%%$#%%%%#$%%$##$#$#$#$#$%#$$#%%%#$%%%$#%%%%#$%%$##$%#$#$%%%$##$#$%%#$%%$##$#$%#$#$%%$##$%#$#$#$%#$$##$%#$%#$#$#$$##$#$#$%#$%#$$#%%#$%#$%#$$##$#$#$#$#$%#$$#%#$#$#$%%#$$##$#$#$#$#$%#$$##$#$#$%#$%#$$##$%#$%#$%#$$##$#$#$#$#$%#$$##$%#$#$%%#$$##$#$#$#$#$%#$$##$#$#$%#$%#$$#%#$%%#$%#$$##$#$#$#$#$%#$$##$#$#$%%%%$#%#$#$%#$%#$$#%#$#$%#$%#$$#%#$#$%#$%#$$

1. 

   A lexer is the power tool for tokenizing. It contains a series of clauses with a regex-like pattern on the left. It matches the longest pattern (not the first pattern). Then it returns the value on the right.

2. 

   lexer creates a func­tion that takes one input port as its argu­ment. Thus, it can be used in the same posi­tions as read or read-char.

3. 

   Special iden­ti­fiers avail­able within lexer rules: lexeme (matched item), input-port (current port being consumed).

4. 

   Ques­tion: without running the code, what will be the result of each tokeniza­tion?

   

   (require brag/support) ; imports `lexer`
   
   (define (apply-port-proc proc str)
     (define ip (open-input-string str))
     (for/list ([tok (in-port proc ip)])
       tok))
   
   (define lex (lexer
                ["fo" lexeme]
                [(:: "f" (:+ "o")) 42]
                [any-char (lex input-port)]))
   
   (apply-port-proc read "foobar")
   (apply-port-proc read-char "foobar")
   (apply-port-proc lex "foobar")
   (apply-port-proc lex "fobar")

   

   (require brag/support) ; imports `lexer`
   
   (define (apply-port-proc proc str)
     (define ip (open-input-string str))
     (for/list ([tok (in-port proc ip)])
       tok))
   
   (define lex (lexer
                ["fo" lexeme]
                [(:: "f" (:+ "o")) 42]
                [any-char (lex input-port)]))
   
   (apply-port-proc read "foobar")
   (apply-port-proc read-char "foobar")
   (apply-port-proc lex "foobar")
   (apply-port-proc lex "fobar")

   
5. 

   Ques­tion (hard): why not just tokenize using cond and regular expres­sions?

6. 

   Lexers are also used for source-code coloring in DrRacket.

tacopocalypse/test.rkt



#lang tacopocalypse
##$%#$%#$#$#$$##$%#$%#$#$#$$##$%#$#$#$%#$$##$#$#$%#$%%$#%#$%#$#$%%$##$#$%%#$%%$##$#$%%#$%%$#%%%%#$%%$##$#$#$#$#$%#$$#%%%#$%%%$#%%%%#$%%$##$%#$#$%%%$##$#$%%#$%%$##$#$%#$#$%%$##$%#$#$#$%#$$##$%#$%#$#$#$$##$#$#$%#$%#$$#%%#$%#$%#$$##$#$#$#$#$%#$$#%#$#$#$%%#$$##$#$#$#$#$%#$$##$#$#$%#$%#$$##$%#$%#$%#$$##$#$#$#$#$%#$$##$%#$#$%%#$$##$#$#$#$#$%#$$##$#$#$%#$%#$$#%#$%%#$%#$$##$#$#$#$#$%#$$##$#$#$%%%%$#%#$#$%#$%#$$#%#$#$%#$%#$$#%#$#$%#$%#$$



#lang tacopoca­lypse
##$%#$%#$#$#$$##$%#$%#$#$#$$##$%#$#$#$%#$$##$#$#$%#$%%$#%#$%#$#$%%$##$#$%%#$%%$##$#$%%#$%%$#%%%%#$%%$##$#$#$#$#$%#$$#%%%#$%%%$#%%%%#$%%$##$%#$#$%%%$##$#$%%#$%%$##$#$%#$#$%%$##$%#$#$#$%#$$##$%#$%#$#$#$$##$#$#$%#$%#$$#%%#$%#$%#$$##$#$#$#$#$%#$$#%#$#$#$%%#$$##$#$#$#$#$%#$$##$#$#$%#$%#$$##$%#$%#$%#$$##$#$#$#$#$%#$$##$%#$#$%%#$$##$#$#$#$#$%#$$##$#$#$%#$%#$$#%#$%%#$%#$$##$#$#$#$#$%#$$##$#$#$%%%%$#%#$#$%#$%#$$#%#$#$%#$%#$$#%#$#$%#$%#$$



 
 
"hello world"
(+ 1 (* 2 (- x)))



 
 
"hello world"
(+ 1 (* 2 (- x)))

tacopocalypse/main.rkt



#lang br/quicklang
(require brag/support) ; imports `lexer`

(module+ reader
  (provide read-syntax))

(define lex
  (lexer
   ;; ···
   ))

(define (tokenize ip)
  (for/list ([tok (in-port lex ip)])
    tok))

(define (parse src toks)
  ;; ···
  )

(define (read-syntax src ip)
  (define toks (tokenize ip))
  (define parse-tree (parse src toks))
  (strip-bindings
   (with-syntax ([PT parse-tree])
     #'(module taco-mod tacopocalypse
         PT))))

(define-macro (my-module-begin PT)
  #'(#%module-begin
     (display (list->string 'PT))))
(provide (rename-out [my-module-begin #%module-begin]))



#lang br/quick­lang
(require brag/support) ; imports `lexer`

(module+ reader
  (provide read-syntax))

(define lex
  (lexer
   ;; ···
   ))

(define (tokenize ip)
  (for/list ([tok (in-port lex ip)])
    tok))

(define (parse src toks)
  ;; ···
  )

(define (read-syntax src ip)
  (define toks (tokenize ip))
  (define parse-tree (parse src toks))
  (strip-bind­ings
   (with-syntax ([PT parse-tree])
     #'(module taco-mod tacopoca­lypse
         PT))))

(define-macro (my-module-begin PT)
  #'(#%module-begin
     (display (list->string 'PT))))
(provide (rename-out [my-module-begin #%module-begin]))

• 1 intro
• 2 taco compiler
• 3 the tacopoca­lypse
• 4 tacogram
• 5 taco victory