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open Camlp4.PreCast
module Caml_syntax = Syntax
let symbols = ref []
let define s =
let i =
try String.index s '='
with Not_found -> failwith ("Invalid symbol definition :" ^ s) in
let symbol = String.sub s 0 i in
let value =
Gram.parse_string
Caml_syntax.expr (Loc.mk "<from-string>") (String.sub s (i + 1) (String.length s - i - 1))
in
symbols := (symbol, value) :: !symbols
EXTEND Caml_syntax.Gram
GLOBAL: Caml_syntax.str_item;
Caml_syntax.str_item: FIRST
[ [ "ifdef"; c = UIDENT; "then"; e1 = SELF;
"else"; e2 = SELF ->
if List.mem_assoc c !symbols then e1 else e2
| "ifdef"; c = UIDENT; "then"; e1 = SELF ->
if List.mem_assoc c !symbols then e1 else <:str_item<>>
| "ifndef"; c = UIDENT; "then"; e1 = SELF;
"else"; e2 = SELF ->
if List.mem_assoc c !symbols then e2 else e1
| "ifndef"; c = UIDENT; "then"; e1 = SELF ->
if List.mem_assoc c !symbols then <:str_item<>> else e1
] ];
END
let expr _ _ s =
try List.assoc s !symbols
with Not_found -> failwith ("No definition for symbol " ^ s)
let _ =
Quotation.add "symbol" Quotation.DynAst.expr_tag expr;
Camlp4.Options.add "-symbol" (Arg.String define)
"<symbol=value> Define a symbol"
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