compiler: fix case on Bool type

[skip bamboo]

cogent/src/Cogent/Desugar.hs

diff --git a/cogent/src/Cogent/Desugar.hs b/cogent/src/Cogent/Desugar.hs
index 5c46e4b..47e1e6d 100644
--- a/cogent/src/Cogent/Desugar.hs
+++ b/cogent/src/Cogent/Desugar.hs
@@ -542,7 +542,8 @@
   desugarExpr $ B.TE (B.getTypeTE e) (S.Let [b1,b2] e) pos
 desugarAlt' e0 (S.PIrrefutable (B.TIP (S.PArrayTake arr ips) pos)) e = __todo "desugarAlts': taking multiple elements out of an array is currently not supported"
 #endif
-desugarAlt' _ _ _ = __impossible "desugarAlt' (_)"  -- literals
+desugarAlt' e0 (S.PBoolLit b) e = desugarExpr e
+desugarAlt' _ _ _ = __impossible "desugarAlt' (_)"  -- literals that cannot be easily exhausted
 
 desugarPrimInt :: B.DepType -> PrimInt
 desugarPrimInt (B.DT (S.TCon "U8"   [] Unboxed)) = U8

cogent/tests/tests/case/pass_case-bool.cogent

diff --git a/cogent/tests/tests/case/pass_case-bool.cogent b/cogent/tests/tests/case/pass_case-bool.cogent
new file mode 100644
index 0000000..0b6098f
--- /dev/null
+++ b/cogent/tests/tests/case/pass_case-bool.cogent
@@ -0,0 +1,3 @@
+foo : Bool -> <T | F>
+foo | True -> F
+    | False -> T