From 0e10313d64f54dd587ebbcd5f413bd999333c911 Mon Sep 17 00:00:00 2001
From: Bruce Hill <bruce@bruce-hill.com>
Date: Sun, 24 Nov 2024 16:13:23 -0500
Subject: Switch `NaN` to be identical to the null value

---
 typecheck.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

(limited to 'typecheck.c')

diff --git a/typecheck.c b/typecheck.c
index 2d84c622..da810258 100644
--- a/typecheck.c
+++ b/typecheck.c
@@ -126,6 +126,28 @@ type_t *parse_type_ast(env_t *env, type_ast_t *ast)
     errx(1, "Unreachable");
 }
 
+static PUREFUNC bool risks_zero_or_inf(ast_t *ast)
+{
+    switch (ast->tag) {
+    case Int: {
+        const char *str = Match(ast, Int)->str;
+        OptionalInt_t int_val = Int$from_str(str);
+        return (int_val.small == 0x1); // zero
+    }
+    case Num: {
+        return Match(ast, Num)->n == 0.0;
+    }
+    case BinaryOp: {
+        auto binop = Match(ast, BinaryOp);
+        if (binop->op == BINOP_MULT || binop->op == BINOP_DIVIDE || binop->op == BINOP_MIN || binop->op == BINOP_MAX)
+            return risks_zero_or_inf(binop->lhs) || risks_zero_or_inf(binop->rhs);
+        else
+            return true;
+    }
+    default: return true;
+    }
+}
+
 PUREFUNC type_t *get_math_type(env_t *env, ast_t *ast, type_t *lhs_t, type_t *rhs_t)
 {
     (void)env;
@@ -1011,6 +1033,16 @@ type_t *get_type(env_t *env, ast_t *ast)
                 return result;
             return Type(NumType, .bits=TYPE_NBITS64);
         }
+        case BINOP_MULT: case BINOP_DIVIDE: {
+            type_t *math_type = get_math_type(env, ast, value_type(lhs_t), value_type(rhs_t));
+            if (value_type(lhs_t)->tag == NumType || value_type(rhs_t)->tag == NumType) {
+                if (risks_zero_or_inf(binop->lhs) && risks_zero_or_inf(binop->rhs))
+                    return Type(OptionalType, math_type);
+                else
+                    return math_type;
+            }
+            return math_type;
+        }
         default: {
             return get_math_type(env, ast, lhs_t, rhs_t);
         }
-- 
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