Chris, What if a runtime tag for type is introduced?
datatype rtti (t@ype) = | Rbool(bool) | Rint(int) and then in Eq: | Eq(bool) of (rtti(a), Expr a, Expr a) during evalution there would be some kind of dynamic check on the tag as well. Another idea is to make [eval] evaluate to some kind of type of values. This type could be represented by a flat tagged union. Then you could do a check on the tag of the union at runtime, and select appropriate function to do the equality checking. Essentially what HX proposed, but with a flat unboxed type representing the values. On Tuesday, October 16, 2018 at 4:51:15 AM UTC+3, Chris Double wrote: > > I have some GADT code that fails at the C compilation stage. It's a > variant of: > > https://gist.github.com/doublec/a3cc8f3431cabe9a319c8e7ba27e7890 > > But the Eq constructor of Expr uses the type index instead of being > 'int' so equality can be done against booleans and ints. The full code > is: > > ----------------8<--------------- > #include "share/atspre_define.hats" > #include "share/atspre_staload.hats" > > datatype Expr(a:t@ype) = > | I(int) of int > | B(bool) of bool > | Add(int) of (Expr int, Expr int) > | Mul(int) of (Expr int, Expr int) > | Eq(bool) of (Expr a, Expr a) > > extern fun{a:t@ype} equals(t1:a, t2:a): bool > implement equals<int>(t1,t2) = g0int_eq(t1,t2) > implement equals<bool>(t1,t2) = eq_bool0_bool0(t1,t2) > > fun{a:t@ype} eval(x:Expr a): a = > case+ x of > | I i => i > | B b => b > | Add (t1, t2) => eval(t1) + eval(t2) > | Mul (t1, t2) => eval(t1) * eval(t2) > | Eq (t1, t2) => equals(t1, t2) > > implement main0() = let > val term1 = Eq(I(5), Add(I(1), I(4))) > val term2 = Mul(I(2), I(4)) > val res1 = eval(term1) > val res2 = eval(term2) > in > println!("res1=", res1, " and res2=", res2) > end > ----------------8<--------------- > > This fails to compile at the C stage with: > > In file included from arith3_dats.c:15:0: > arith3_dats.c: In function ‘eval_2__2__1’: > arith3_dats.c:1098:24: error: ‘PMVtmpltcstmat’ undeclared (first use > in this function) > ATSINSmove(tmpret2__1, > PMVtmpltcstmat[0](equals<S2EVar(5554)>)(tmp9__1, tmp10__1)) ; > ^ > ATS2-Postiats-0.3.11//ccomp/runtime/pats_ccomp_instrset.h:276:37: > note: in definition of macro ‘ATSINSmove’ > #define ATSINSmove(tmp, val) (tmp = val) > .... > > Any thoughts on what I'm doing wrong? > > -- > https://bluishcoder.co.nz > -- You received this message because you are subscribed to the Google Groups "ats-lang-users" group. To unsubscribe from this group and stop receiving emails from it, send an email to ats-lang-users+unsubscr...@googlegroups.com. To post to this group, send email to ats-lang-users@googlegroups.com. Visit this group at https://groups.google.com/group/ats-lang-users. To view this discussion on the web visit https://groups.google.com/d/msgid/ats-lang-users/3fa603b6-eda2-4f0e-b5ff-b69ff2ed6c27%40googlegroups.com.
