Example of negation in gyp

shell log

fischman@fischman-linux ~/t $ GYP_DEFINES="base=0" GYP_GENERATORS=ninja ~/src/chromium/src/tools/gyp/gyp --depth=. t.gyp  && grep NEGATION out/Default/obj/MyTarget.ninja 
cflags = -DNEGATION_1
fischman@fischman-linux ~/t $ GYP_DEFINES="base=1" GYP_GENERATORS=ninja ~/src/chromium/src/tools/gyp/gyp --depth=. t.gyp  && grep NEGATION out/Default/obj/MyTarget.ninja 
cflags = -DNEGATION_0

t.gyp

{
    'variables': {
      'variables': {
        'base%': 1,
      },
      'base%': '<(base)',
      'negation%': '1 - <(base)',
    },

  'targets': [
    {
      'target_name': 'MyTarget',
      'type': 'executable',
      'sources': [ 'MyTarget.c' ],
      'conditions': [
        ['<(negation)==1', {
          'cflags': [ '-DNEGATION_1' ],
        }, {
          'cflags': [ '-DNEGATION_0' ],
        }],
      ],
    },
  ],
}