Essentials of Programming Languages Language

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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