Regression test for infinite regress in executor

This test will fail if laziness doesn't prevent infinite recursion in
the executor. It's implemented using `expect` instead of `timeout` in
the hope that it will make life easier for non-GNU systems.

.travis.yml

@@ -6,6 +6,8 @@ before_install:
   - sudo apt-get install -qq libghc-unordered-containers-dev libghc-mtl-dev libghc-network-dev libghc-xml-dev libghc-transformers-dev libghc-text-dev libghc-utf8-string-dev libghc-vector-dev libghc-split-dev libghc-ansi-terminal-dev libghc-ansi-wl-pprint-dev
   # trifecta dependencies
   - sudo apt-get install -qq libghc-blaze-builder-dev libghc-blaze-html-dev libghc-data-lens-dev libghc-bifunctors-dev libghc-hashable-dev libghc-semigroups-dev libghc-semigroupoids-dev libghc-parallel-dev libghc-comonad-dev libghc-terminfo-dev libghc-keys-dev
+  # test dependency
+  - sudo apt-get install -qq expect
 install:
   - cabal install -f FFI -f LLVM --only-dependencies --enable-tests
 before_script:

test/reg039/expected

@@ -0,0 +1,2 @@
+Type checking ./reg039.idr
+[3, 2, 1]

test/reg039/reg039.idr

@@ -0,0 +1,12 @@
+module LazyExec
+
+-- The regression that this tests for is broken laziness in the executor.
+
+covering
+countdown : Int -> Lazy (List Int)
+countdown n = if n > 0
+                 then (n :: countdown (n-1))
+                 else []
+
+go : IO ()
+go = putStrLn $ show (Force (countdown 3))

test/reg039/run

@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+
+# From http://unix.stackexchange.com/questions/43340/how-to-introduce-timeout-for-shell-scripting
+# Executes command with a timeout
+# Params:
+#   $1 timeout in seconds
+#   $2 command
+# Returns 1 if timed out 0 otherwise
+timeout() {
+
+    time=$1
+
+    # start the command in a subshell to avoid problem with pipes
+    # (spawn accepts one command)
+    command="/bin/sh -c \"$2\""
+
+    expect -c "set echo \"-noecho\"; set timeout $time; spawn -noecho $command; expect timeout { exit 1 } eof { exit 0 }"
+
+    if [ $? = 1 ] ; then
+        echo "Timeout after ${time} seconds"
+    fi
+
+}
+
+timeout 60 "idris $@ --nocolour reg039.idr --exec go"
+rm -f reg039 *.ibc