Wanna use JSON syntax in Felix? Here we go:
(1) Write the grammar
// lib/grammar/json.flxh
syntax json {
requires expressions;
x[sapplication_pri] := "json" "(" json_value ")" =># "_3";
json_object : string = "{" "}";
json_object : string = "{" json_members "}";
json_members : string = json_pair ( "," json_pair ) *;
json_pair : string = strstring ":" json_value;
json_array : string = "[" "]";
json_array : string = "[" json_elements "]";
json_elements : string = json_value ( "," json_value ) *;
json_value : string =
| strstring
| json_number
| json_object
| json_array
| "true"
| "false"
| "null"
;
json_number : string =
| strint
| strfloat
;
}
(2) add the file to the files list:
// lib/grammar/grammar.files
grammar/grammar_scheme_support.flx
grammar/expressions.flxh
grammar/texsyms.flxh
grammar/patterns.flxh
grammar/functions.flxh
grammar/statements.flxh
grammar/variables.flxh
grammar/macros.flxh
grammar/cbind.flxh
grammar/executable.flxh
grammar/assignment.flxh
grammar/control.flxh
grammar/conditional.flxh
grammar/loops.flxh
grammar/requirements.flxh
grammar/type_decls.flxh
grammar/assertions.flxh
grammar/namespaces.flxh
grammar/regexps.flxh
grammar/cgram.flxh
grammar/json.flxh <-----
grammar/felix.flxh
grammar/save.flxh
(3) Make it part of Felix:
syntax felix {
requires
statements,
type_decls,
variables,
executable,
assignment,
control,
conditional,
loops,
assertions,
namespaces,
requirements,
expressions,
texsyms,
functions,
patterns,
cbind,
regexps,
macros,
json <----------
;
}
(4) delete lib/grammar/syntax.automaton
(5) Run a test program:
// jt.flx
val x = json ( [true, 12_3.4, 'Hello', {"HI": 1, "LO":2}, null] );
println$ x;
~/felix>flx --test=build/release --force jt
Deprecated Scheme string [ true , 123.4 , "Hello" , { "HI" : 1 , "LO" : 2 } ,
null ]' as Felix string
[ true , 123.4 , "Hello" , { "HI" : 1 , "LO" : 2 } , null ]
(6) Ignore the "Deprecated Scheme string thing .. small bug to fix ..
(7) Time to party!
It's that easy. String grammars translate syntax into strings. The result is
just
an ordinary string. But it is one which is syntax checked by the Felix parser.
Note that by luck, Felix numbers and strings can be used, but the representation
is normalised to something which, by luck, is close to what JSON actually
requires.
--
john skaller
[email protected]
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