Not much to say about this one. A parser crash. Easiest way to reproduce:
[⍬]
non-ASCII char in C-String '⍬'
==============================================================================
Assertion failed: 0 && "Bad C-string"
in Function: UCS_string
in file: UCS_string.cc:93
Call stack:
----------------------------------------
-- Stack trace at UCS_string.cc:93
----------------------------------------
0x7FA4229AF1A3 __libc_start_main
0x46E075 main
0x5C7DD5 Workspace::immediate_execution(bool)
0x4BACB9 Command::process_line()
0x4BB644 Command::do_APL_expression(UCS_string&)
0x4BAD31 Command::finish_context()
0x4C3967 Executable::execute_body() const
0x56E4D1 StateIndicator::run()
0x4F4144 Prefix::reduce_statements()
0x4F005E Prefix::syntax_error(char const*)
0x4C3888 throw_apl_error(ErrorCode, char const*)
0x4C378B Error::update_error_info(StateIndicator*)
0x4C3F35 Executable::set_error_info(Error&, Function_PC2) const
0x5A148E Token::error_info(UCS_string&) const
0x5A1040 Token::canonical(PrintStyle) const
0x50ED5E PrintBuffer::PrintBuffer(Value const&, PrintContext const&, std::ostream*)
0x50CC67 PrintBuffer::pb_empty(Value const&, PrintContext, PrintStyle)
0x5A97DF UCS_string::UCS_string(char const*)
0x482845 do_Assert(char const*, char const*, char const*, int)
========================================
SI stack:
Depth: 3
Exec: 0x1bcef00
Safe exec: 0
Pmode: ◊ [⍬]
PC: 4 (5) RETURN_STATS
Stat: [⍬]
err_code: 0x0
Depth: 2
Exec: 0x1bcd510
Safe exec: 0
Pmode: ◊ []
PC: 3 (4) RETURN_STATS
Stat: []
err_code: 0x20002
thrown at: Prefix.cc:459
e_msg_1: 'SYNTAX ERROR'
e_msg_2: ' []'
e_msg_3: ' ^'
Depth: 1
Exec: 0x1bca690
Safe exec: 0
Pmode: ◊ [0]
PC: 4 (5) RETURN_STATS
Stat: [0]
err_code: 0x20002
thrown at: Prefix.cc:459
e_msg_1: 'SYNTAX ERROR'
e_msg_2: ' [0]'
e_msg_3: ' ^'
Depth: 0
Exec: 0x1bccfa0
Safe exec: 0
Pmode: ◊ (3 4 ⍴ 10+⍳12)[1;4]
PC: 13 (15) ENDL
Stat: (3 4 ⍴ 10+⍳12)[1;4]
err_code: 0x50005
thrown at: Value.cc:1134
e_msg_1: 'INDEX ERROR'
e_msg_2: ' (3 4⍴10+⍳12)[1;4]'
e_msg_3: ' ^ ^'
==============================================================================