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Essentials of Programming Languages Language
define-datatype
cases
sllgen: make-string-scanner
sllgen: make-string-parser
sllgen: make-stream-parser
sllgen: make-define-datatypes
sllgen: show-define-datatypes
sllgen: list-define-datatypes
sllgen: make-rep-loop
eopl: error
eopl: printf
eopl: pretty-print
list-of
always?
maybe
empty
time
collect-garbage
trace
untrace
provide
eopl: error-stop
install-eopl-exception-handler
Bibliography

6.5
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## Essentials of Programming Languages Language

The Essentials of Programming Languages language in DrRacket provides a subset of functions and syntactic forms of racket—mostly the ones that correspond to r5rs forms. See below for a complete list. The language is intended for use with the textbook [EoPL].

#lang eopl | package: eopl

The following bindings are re-provided from racket:

| make-parameter |  | * |  | inexact?
| parameterize |  | / |  | zero?
| print-struct |  | abs |  | positive?
| unquote |  | gcd |  | negative?
| unquote-splicing |  | lcm |  | odd?
| quote |  | exp |  | even?
| quasiquote |  | log |  | quotient
| if |  | sin |  | remainder
| lambda |  | cos |  | modulo
| letrec |  | tan |  | floor
| define-syntax |  | not |  | ceiling
| delay |  | eq? |  | truncate
| let |  | make-string |  | round
| let* |  | symbol->string |  | numerator
| let-syntax |  | string->symbol |  | denominator
| letrec-syntax |  | make-rectangular |  | asin
| and |  | exact->inexact |  | acos
| or |  | inexact->exact |  | atan
| cond |  | number->string |  | sqrt
| case |  | string->number |  | expt
| do |  | rationalize |  | make-polar
| begin |  | output-port? |  | real-part
| set! |  | current-input-port |  | imag-part
| #%module-begin |  | current-output-port |  | angle
| #%app |  | current-error-port |  | magnitude
| #%datum |  | open-input-file |  | input-port?
| #%top |  | open-output-file |  | read
| #%top-interaction |  | close-input-port |  | read-char
| #%require |  | close-output-port |  | peek-char
| #%provide |  | with-output-to-file |  | eof-object?
| #%expression |  | flush-output |  | char-ready?
| syntax-rules |  | string-length |  | write
| ... |  | string-ci<=? |  | display
| cons |  | string-ci>=? |  | newline
| car |  | string-append |  | write-char
| cdr |  | string-fill! |  | load
| pair? |  | string->list |  | string?
| map |  | list->string |  | string
| for-each |  | vector-length |  | string-ref
| caar |  | vector-fill! |  | string-set!
| cadr |  | vector->list |  | string=?
| cdar |  | list->vector |  | substring
| cddr |  | char-alphabetic? |  | string-copy
| caaar |  | char-numeric? |  | string-ci=?
| caadr |  | char-whitespace? |  | string<?
| cadar |  | char-upper-case? |  | string>?
| caddr |  | char-lower-case? |  | string<=?
| cdaar |  | char->integer |  | string>=?
| cdadr |  | integer->char |  | string-ci<?
| cddar |  | char-downcase |  | string-ci>?
| cdddr |  | call-with-output-file |  | vector?
| caaaar |  | call-with-input-file |  | make-vector
| caaadr |  | with-input-from-file |  | vector
| caadar |  | apply |  | vector-ref
| caaddr |  | symbol? |  | vector-set!
| cadaar |  | null? |  | char?
| cadadr |  | list? |  | char=?
| caddar |  | list |  | char<?
| cadddr |  | length |  | char>?
| cdaaar |  | append |  | char<=?
| cdaadr |  | reverse |  | char>=?
| cdadar |  | list-tail |  | char-ci=?
| cdaddr |  | list-ref |  | char-ci<?
| cddaar |  | memq |  | char-ci>?
| cddadr |  | memv |  | char-ci<=?
| cdddar |  | member |  | char-ci>=?
| cddddr |  | assq |  | char-upcase
| = |  | assv |  | boolean?
| < |  | assoc |  | eqv?
| > |  | procedure? |  | equal?
| <= |  | number? |  | force
| >= |  | complex? |  | call-with-values
| max |  | real? |  | values
| min |  | rational? |  | dynamic-wind
| + |  | integer? |  | eval
| - |  | exact? |  |

> > syntax
> > (define-datatype id predicate-id
> > (variant-id (field-id predicate-expr) ...)
> > ...)

Defines the datatype id and a function predicate-id that returns #t for instances of the datatype, and #f for any other value.

Each variant-id is defined as a constructor function that creates an instance of the datatype; the constructor takes as many arguments as the variant’s field-ids, and each argument is checked by applying the function produced by the variant’s predicate-expr.

In DrScheme v209 and older, when constructor-based printing was used, variant instances were printed with a make- prefix before the variant name. Thus, for compatibility, in addition to variant-id, make-variant-id is also defined for each variant-id (to the same constructor as variant-id).

> > syntax
> > (cases datatype-id expr
> > (variant-id (field-id ...) result-expr ...)
> > ...)
> (cases datatype-id expr
> (variant-id (field-id ...) result-expr ...)
> ...
> (else result-expr ...))

Branches on the datatype instance produced by expr, which must be an instance of the specified datatype-id that is defined with define-datatype.

> syntax sllgen:make-string-scanner
> syntax sllgen:make-string-parser
> syntax sllgen:make-stream-parser
> syntax sllgen:make-define-datatypes
> syntax sllgen:show-define-datatypes
> syntax sllgen:list-define-datatypes

Defined in the textbook’s Appendix B [EoPL]. However, the DrRacket versions are syntactic forms, instead of procedures, and the arguments must be either quoted literal tables or identifiers that are defined (at the top level) to quoted literal tables.

> value sllgen:make-rep-loop : procedure?

Defined in the EoPL textbook’s Appendix B [EoPL] (and still a function).

> value eopl:error : procedure?

As in the book.

> procedure (eopl:printf form v ...) → void?
> form : string?
> v : any/c
> procedure (eopl:pretty-print v [port]) → void?
> v : any/c
> port : output-port? = (current-output-port)

Same as scheme/base’s printf and pretty-print.

> procedure ((list-of pred ...+) x) → boolean?
> pred : (any/c . -> . any)
> x : any/c
> procedure (always? x) → boolean?
> x : any/c
> procedure (maybe pred) → boolean?
> pred : (any/c . -> . boolean?)

As in the book [EoPL].

> value empty : empty?

The empty list.

> syntax (time expr)

Evaluates expr, and prints timing information before returning the result.

> procedure (collect-garbage) → void?

Performs a garbage collection (useful for repeatable timings).

> syntax (trace id ...)
> syntax (untrace id ...)

For debugging: trace redefines each id at the top level (bound to a procedure) so that it prints arguments on entry and results on exit. The untrace form reverses the action of trace for the given ids.

Tracing a function causes tail-calls in the original function to become non-tail calls.

> syntax (provide provide-spec ...)

Useful only with a module that uses eopl as a language: exports identifiers from the module. See provide from racket for more information.

> value eopl:error-stop : (-> any/c)

Defined only in the top-level namespace (i.e., not in a module); mutate this variable to install an exception-handling thunk. Typically, the handler thunk escapes through a continuation.

The eopl library sets this variable to #f in the current namespace when it executes.

> procedure (install-eopl-exception-handler) → void?

Sets an exception handler to one that checks eopl:error-stop.

The eopl library calls this function when it executes.

### Bibliography

[EoPL] |  | “Essentials of Programming Languages, Third Edition,” MIT Press, 2008. http://www.eopl3.com/

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