Exploring W behavior in the REPL

The REPL compiles each entry into executable memory and runs it
immediately; definitions persist across entries. It reads stdin, so it is
fully scriptable.

Setup and scripting

./bin/wv2 repl.w -o bin/repl     # then ./bin/repl attaches a prompt
printf 'print(c"hi\\x0a")\n:quit\n' | ./bin/repl

Piped input keeps explicit tabs; a line ending in : opens a block and a
blank line closes it (Python-style):

printf 'int twice(int n):\n\treturn n * 2\n\ntwice(21)\n:quit\n' | ./bin/repl

• A bare expression echoes its value.
• Top-level declarations become persistent globals; redefining a name
  shadows the old binding.
• A bad entry rolls back via checkpoint instead of killing the process,
  so one typo does not end the session.
• ./bin/repl file.w [args...] compiles and runs a program first, then
  attaches the prompt to its live definitions (--no_main skips main)
  — useful for poking at a program's functions interactively.
• :quit exits (always end piped input with it), :help lists commands.

Programmatic alternative: the w-toolchain MCP server's repl_eval tool
takes entries: string[] and returns captured output.