Add [make versions].

.gitignore

@@ -2,3 +2,4 @@
 inferno.install
 .merlin
 _build
+dune-workspace.versions

Makefile

@@ -52,6 +52,40 @@ pin:
 unpin:
 	@ opam pin remove $(THIS)
 
+# [make versions] compiles Inferno under many versions of OCaml, whose
+# list is specified below.
+
+# This requires appropriate opam switches to exist. A missing switch
+# can be created like this:
+#   opam switch create 4.03.0
+
+VERSIONS := \
+  4.08.1 \
+  4.09.1 \
+  4.09.0+bytecode-only \
+  4.10.0 \
+  4.11.1 \
+  4.12.0 \
+  4.13.0 \
+
+.PHONY: versions
+versions:
+	@(echo "(lang dune 2.0)" && \
+	  for v in $(VERSIONS) ; do \
+	    echo "(context (opam (switch $$v)))" ; \
+	  done) > dune-workspace.versions
+	@ dune build --workspace dune-workspace.versions @all
+
+.PHONY: handiwork
+handiwork:
+	@ current=`opam switch show` ; \
+	  for v in $(VERSIONS) ; do \
+	    opam switch $$v && \
+	    eval $$(opam env) && \
+	    opam install --yes qcheck-alcotest ; \
+	  done ; \
+	  opam switch $$current
+
 HEADACHE := headache
 LIBHEAD  := $(shell pwd)/headers/library-header
 FIND     := $(shell if command -v gfind >/dev/null ; then echo gfind ; else echo find ; fi)