build(Makefile): fix shell and ghci targets for entrypoint

Makefile

@@ -3,6 +3,9 @@ export SHELL=bash
 export CLEAN_DEPENDENCIES ?= false
 export CLEAN_IMAGES ?= false
 
+export ENTRYPOINT ?= bash
+export SRC
+
 .PHONY: help
 # HELP: print out this help message
 help:
@@ -79,11 +82,11 @@ start-%:
 .PHONY: shell-%
 # HELP(shell-$SERVICE): launch a (bash) shell inside a given service
 shell-%:
-	docker compose run --build --no-deps $* bash
+	docker compose run --build --no-deps --entrypoint="$(ENTRYPOINT)" $*
 .PHONY: ghci
-# HELP: launch ghci
-ghci:
-	docker compose run --build --no-deps backend stack ghci $(SRC)
+# HELP: launch ghci instance. Use in combination with SRC to specify the modules to be loaded by ghci: make ghci SRC=src/SomeModule.hs
+ghci: ENTRYPOINT=stack ghci $(SRC)
+ghci: shell-backend ;
 
 .PHONY: stop
 # HELP: stop all services