-- mapped_f must be a CoreExpr (since we can't represent functions as VHDL
-- expressions). arg must be a CoreExpr (and should be a CoreSyn.Var), since
-- we must index it (which we couldn't if it was a VHDL Expr, since only
-- mapped_f must be a CoreExpr (since we can't represent functions as VHDL
-- expressions). arg must be a CoreExpr (and should be a CoreSyn.Var), since
-- we must index it (which we couldn't if it was a VHDL Expr, since only