C compiler warning when using match

[justinethier]

Consider the following example:

(import (scheme base)
        (scheme read)
        (cyclone match))

(match
  (read)
  (else
   'done))

This produces the following warning when compiled:

test.c: In function '__lambda_1':
test.c:438:3: warning: statement with no effect [-Wunused-value]
   &c_73993;__halt(__halt(obj_int2obj(0)));;

It seems the problem is that there is a continuation to handle the case when there is match, but when there is an else this continuation will never be called.

TBD if match can be enhanced to generate better code in this case.

Regardless, our compiler should not be generating C statements with no effect.

[justinethier]

Here is a simplified program leading to the same (or at least very similar) compilation warning:

((lambda (failure)
    ((lambda (else) 'done) 'v))
  (lambda () (error 'match "no matching pattern")))

[justinethier]

This program is equivalent to the original match example:

(((lambda (v)
    ((lambda (failure)
       ((lambda (else) 'done) v))
     (lambda () (error 'match "no matching pattern"))))
  (read)))

Seems ultimately this is not an issue with match but rather with the compiler itself.

[justinethier]

Updated the compiler to no longer emit code containing unused closures.