I'm debating trying to use something like define-datatype, as used in
EOPL and PLAI (and available in the Racket languages that support those
books) early in my first-year undergraduate class. (Opinions on the
wisdom of this, or on my sanity in general, by direct e-mail, please.)
In a teaching-language program, just using `require' to include
define-datatype and type-case or 'cases' from plai/datatype.rkt or
eopl/datatype.rkt appears to work so long as the teaching language is
ISL or higher. In BSL or BSL+, I seem to be running into a thicket of
rules designed to protect students. I'm using as my exploratory example
the trivial arithmetic expression evaluator from the beginning of PLAI
(2007 edition). Using plai/datatype.rkt generates an error because a use
of define-datatype involves function names in expression positions (as
contracts for field names). If I wrap these in applications of
first-order->higher-order from lang/prim, which seems to be designed for
this task, I get an error the first time I try to use a variant
constructor (in the PLAI example, in 'parse'). The constructors seem to
be defined, but also seem to be regarded as variables instead of
functions. This is also what happens with eopl/datatype.rkt (the other
error does not seem to arise).
Do I have a hope of pulling this off, and if so, how? Many thanks. --PR
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