[GiNaC-list] Adding custom functions to the parser

[Vitaly Magerya]

Hi, all. I'm trying to add custom functions to GiNaC::parser in
a way similar to how it's done in default_reader.cpp:

#include <ginac/ginac.h>
#include <ginac/parser.h>
#include <iostream>
#include <sstream>
#include <string>

static GiNaC::ex sqrt_reader(const GiNaC::exvector& ev)
{ return GiNaC::sqrt(ev[0]); }

int main() {
    std::string input = "sqrt(4)";
    std::istringstream instream(input);
    auto proto = GiNaC::prototype_table();
    proto[std::make_pair("sqrt", 1)] = sqrt_reader;
    auto symtab = GiNaC::symtab();
    auto reader = GiNaC::parser(symtab, false, proto);
    GiNaC::ex expr = reader(instream);
    std::cout << input << " = " << expr << "\n";
}

This unfortunately crashes before entering sqrt_reader. Here's a backtrace:

#0  GiNaC::function::eval (this=0x7fffffffcd10) at function.cpp:1450
#1  0x000000000045c212 in GiNaC::ex::construct_from_basic (other=...)
at ex.cpp:309
#2  0x000000000059e0d5 in GiNaC::ex::ex (other=...,
this=0x7fffffffcc50) at ./ex.h:268
#3  GiNaC::dispatch_reader_fcn (args=std::vector of length 1, capacity
1 = {...}, ptr=<optimized out>) at parser/parser.cpp:62
#4  GiNaC::parser::parse_identifier_expr (this=<optimized out>) at
parser/parser.cpp:103
#5  0x000000000059db7d in GiNaC::parser::parse_primary
(this=this at entry=0x7fffffffd310) at parser/parser.cpp:173
#6  0x000000000059dc3f in GiNaC::parser::parse_expression
(this=this at entry=0x7fffffffd310) at parser/parser.cpp:194
#7  0x000000000059e919 in GiNaC::parser::operator()
(this=0x7fffffffd310, input=...) at parser/parser.cpp:226
#8  0x0000000000423e35 in main () at parsingcrash.cpp:21

Can anyone tell me how to do this correctly?