title: Makefile - How to check if variable is not empty and is one of the two values
body: <p>I am trying to check if my <code>ENVIRONMENT</code> variable is not empty and is either <code>development</code> or <code>production</code>.</p>
  
  <pre><code>ENVIRONMENT ?= development
  
  define ENV_CHECK
         $(if $(or $(call seq,$(1),development),$(call seq,$(1),production)),true,false)
  endef
  
  .PHONY: test
  test:
         @echo "$(ENVIRONMENT)"
         $(call ENV_CHECK,$(ENVIRONMENT))
  </code></pre>
  
  <p>My <code>make test</code> fails with below error</p>
  
  <pre><code># make test
  development
  false
  make: *** [test] Error 1
  </code></pre>