bug.nim

# to build this with emscripten, you need emsdk on your PATH.
# first, clone https://github.com/emscripten-core/emsdk
# then in that repo run:
# ./emsdk install latest
# ./emsdk activate latest
# and then add the directories it prints out to your PATH
#
# then in this repo run:
# nim c -d:emscripten bug.nim
#
# finally, run an http server:
# python -m http.server
#
# in your browser console, you'll see:
# Error: unhandled exception: key not found: (-1, -1) [KeyError]

import tables

type
  DirectionName = enum
    West, NorthWest, North, NorthEast,
    East, SouthEast, South, SouthWest,

const
  velocities = {(-1, 0): West, (-1, -1): NorthWest,
                (0, -1): North, (1, -1): NorthEast,
                (1, 0): East, (1, 1): SouthEast,
                (0, 1): South, (-1, 1): SouthWest}.toTable

echo velocities[(-1, -1)]

config.nims

when defined(emscripten):
  # This path will only run if -d:emscripten is passed to nim.

  --nimcache:tmp # Store intermediate files close by in the ./tmp dir.

  --os:linux # Emscripten pretends to be linux.
  --cpu:wasm32 # Emscripten is 32bits.
  --cc:clang # Emscripten is very close to clang, so we ill replace it.
  when defined(windows):
    --clang.exe:emcc.bat  # Replace C
    --clang.linkerexe:emcc.bat # Replace C linker
    --clang.cpp.exe:emcc.bat # Replace C++
    --clang.cpp.linkerexe:emcc.bat # Replace C++ linker.
  else:
    --clang.exe:emcc  # Replace C
    --clang.linkerexe:emcc # Replace C linker
    --clang.cpp.exe:emcc # Replace C++
    --clang.cpp.linkerexe:emcc # Replace C++ linker.
  --listCmd # List what commands we are running so that we can debug them.

  --gc:arc # GC:arc is friendlier with crazy platforms.
  --exceptions:goto # Goto exceptions are friendlier with crazy platforms.

  --define:useMalloc

  # Pass this to Emscripten linker to generate html file scaffold for us.
  switch("passL", "-o index.html -s INITIAL_MEMORY=64MB -s SAFE_HEAP=1 -s WARN_UNALIGNED=1 -s USE_WEBGL2=1")