@margin-note{This is a fork of the @link["https://docs.racket-lang.org/ragg"]{@racket[ragg]} package. It has a variety of bugfixesand new features. Some of these features have required new notation that's not necessarily compatible with all existing @racket[ragg] files.
@ -77,11 +77,11 @@ This BNF description is also known as a @deftech{grammar}. Just as it does in a
Have we made progress? We have a valid grammar. But we're still missing a @emph{parser}: a function that can use that description to make structures out of a sequence of tokens.
Meanwhile, it's clear that we don't yet have a valid program because there's no @litchar{#lang} line. Let's add one: put @litchar{#lang brag} at the top of the grammar, and save it as a file called @filepath{nested-word-list.rkt}.
Meanwhile, it's clear that we don't yet have a valid program because there's no @litchar{#lang} line. Let's add one: put @litchar{#lang yaragg} at the top of the grammar, and save it as a file called @filepath{nested-word-list.rkt}.
@filebox["nested-word-list.rkt"]{
@verbatim{
#lang brag
#lang yaragg
nested-word-list: WORD
| LEFT-PAREN nested-word-list* RIGHT-PAREN
}}
@ -151,7 +151,7 @@ to use:
@itemize[
@item{It provides a @litchar{#lang} for writing BNF grammars.
A module written in @litchar{#lang brag} automatically generates a
A module written in @litchar{#lang yaragg} automatically generates a
parser. The grammar controls the structure of the syntax objects it generates.}
@item{The language uses a few conventions to simplify the expression of
@ -226,7 +226,7 @@ Here's a first pass at expressing the structure of these line-drawing programs.
@filebox["simple-line-drawing.rkt"]{
@verbatim|{
#lang brag
#lang yaragg
drawing: rows*
rows: repeat chunk+ ";"
repeat: INTEGER
@ -674,7 +674,7 @@ generates.
@subsection[#:tag "brag-syntax"]{Syntax and terminology}
A program in the @tt{brag} language consists of the language line
@litchar{#lang brag}, followed by a collection of @tech{rule}s and
@litchar{#lang yaragg}, followed by a collection of @tech{rule}s and
possibly @tech{line comment}s or @tech{multiline comment}s.
A @deftech{rule} is a sequence consisting of: a @tech{rule identifier}, a separator (either @litchar{":"} or @litchar{"::="}), and a @tech{pattern}.
@ -726,7 +726,7 @@ A @deftech{pattern} is one of the following:
For example, in the following program:
@nested[#:style 'inset
@verbatim|{
#lang brag
#lang yaragg
;; A parser for a silly language
sentence: verb optional-adjective object
verb: greeting
@ -749,7 +749,7 @@ More examples:
BNF for binary
strings that contain an equal number of zeros and ones.
@verbatim|{
#lang brag
#lang yaragg
equal: [zero one | one zero] ;; equal number of "0"s and "1"s.
zero: "0" equal | equal "0" ;; has an extra "0" in it.
one: "1" equal | equal "1" ;; has an extra "1" in it.
@ -784,7 +784,7 @@ If the cut is applied to a right-hand pattern element, then that element is omit
For instance, consider this simple grammar for arithmetic expressions:
@verbatim|{
#lang brag
#lang yaragg
expr : term ('+' term)*
term : factor ('*' factor)*
factor : ("0" | "1" | "2" | "3"
@ -803,7 +803,7 @@ We get this parse tree:
Suppose we felt the @litchar{+} and @litchar{*} characters were superfluous. We can add cuts to the grammar by prefixing these pattern elements with @litchar{/}:
@verbatim|{
#lang brag
#lang yaragg
expr : term (/'+' term)*
term : factor (/'*' factor)*
factor : ("0" | "1" | "2" | "3"
@ -818,7 +818,7 @@ Our parse tree changes accordingly:
Now suppose we apply a cut on the rule name, @racket[factor]:
@verbatim|{
#lang brag
#lang yaragg
expr : term (/'+' term)*
term : factor (/'*' factor)*
/factor : ("0" | "1" | "2" | "3"
@ -839,7 +839,7 @@ If the splice is applied to a right-hand pattern element, that element is splice
Suppose we remove the cut from the @racket[factor] rule name and instead splice the second appearance of @racket[factor] in the pattern for the @racket[term] rule:
@verbatim|{
#lang brag
#lang yaragg
expr : term (/'+' term)*
term : factor (/'*' @factor)*
factor : ("0" | "1" | "2" | "3"
@ -854,7 +854,7 @@ The @racket[factor] elements matching the first position of the @racket[term] pa
Finally, suppose we add a splice to the @racket[term] rule name:
@verbatim|{
#lang brag
#lang yaragg
expr : term (/'+' term)*
@term : factor (/'*' @factor)*
factor : ("0" | "1" | "2" | "3"
@ -875,7 +875,7 @@ Caveat for the top-level rule: though the rule name can have a cut, it cannot ha
@subsection{Syntax errors}
Besides the basic syntax errors that can occur with a malformed grammar, there
are a few other classes of situations that @litchar{#lang brag} will consider
are a few other classes of situations that @litchar{#lang yaragg} will consider
as syntax errors.
@tt{brag} will raise a syntax error if the grammar:
@ -888,7 +888,7 @@ as syntax errors.
following program:
@nested[#:style 'code-inset
@verbatim|{
#lang brag
#lang yaragg
foo: [bar]
}|
]
@ -904,7 +904,7 @@ as syntax errors.
program:
@nested[#:style 'code-inset
@verbatim|{
#lang brag
#lang yaragg
infinite-a: "a" infinite-a
}|
]
@ -918,7 +918,7 @@ grammars.
@subsection{Semantics}
A program written in @litchar{#lang brag} produces a module that provides a few
A program written in @litchar{#lang yaragg} produces a module that provides a few
bindings. The most important of these is @racket[parse]:
@defproc[(parse [source-path any/c #f]
@ -994,7 +994,7 @@ Thus, it's only the presence of @tech{rule identifier}s in a rule's
Jack Firth
2 years ago