Added scopes test to see things more clearly

tests/scopes/Makefile

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+CATALA_LANG=en
+SRC=scopes.catala
+
+include ../Makefile.common

tests/scopes/scopes.catala

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+/*
+
+declaration structure Child :
+  data date_of_birth content date
+  data age content integer
+
+declaration scope ChildWellFormed :
+  context child content Child
+
+scope ChildWellFormed :
+  definition age equals years of (now - date_of_birth)
+
+declaration scope ChildBenefit :
+  context child content Child
+  context child_well_formed scope ChildWellFormed
+
+scope ChildBenefit :
+  definition child_well_formed.date_of_birth equals |01/01/2000|
+  definition child equals child_well_formed.child
+
+# To what is this translating to ?
+# ChildWellFormed translates to
+# (child.date_of_birth * child.age) -> (child.date_of_birth * child.age)
+
+# So what will the implementation of ChildBenefit look like in the lambda calculus?
+#
+# let ChildWellFormed (
+#   child.date_of_birth, child.age, child.child_well_formed, child_well_formed.age
+# ) =
+# let child_well_formed.age = 12 in
+# let (child_well_formed.date_of_birth, child_well_formed.age) = child_well_formed (
+#   child.child_well_formed, child_well_formed.age
+# ) in
+# let (child.date_of_birth, child.age) =
+#   (child_well_formed.date_of_birth, child_well_formed.age)
+# in
+# (child.date_of_birth, child.age)
+
+# We can see that definitions in the caller scope can either :
+# - set a parameter of the callee scope
+# - retrieve a result of the caller scope
+# In the caller scope, uses of callee scope variables should correspond
+# to uses of the result of these variables after calling the scope, while
+# callee scope variable definitions should correspond to callee scope parameter
+# setting before the call.
+
+# But setting a parameter of the callee scope can conflict with a definition of
+# this parameter inside the callee scope.
+
+scope ChildBenefit :
+  definition child_well_formed.age equals 12
+
+# How do we resolve things now ? Do we have
+# - child_well_formed.age = 12 or
+# - child_well_formed.age = years of (now - child_well_formed.date_of_birth) ?
+#
+# Well the answer to this question lies in default logic! More precisely, we have
+# to pick a precedence order between definitions of the caller scope and definitions
+# of the caller scope. Because the law sometimes says things like :
+#
+# "compute this benefit like mentionned at article XXX but change the threshold
+#  Foo to $ZZZZZ."
+#
+# The meaningful semantics to give here is that caller scope definition should
+# have higher precedence on callee scope definitions.
+*/