Merge pull request #2354 from rtfeldman/add_builtin_Num.minI128

Add `Num.minI128` builtin

compiler/builtins/docs/Num.roc

@@ -65,6 +65,7 @@ interface Num
             maxI128,
             maxInt,
             minFloat,
+            minI128,
             minInt,
             modInt,
             modFloat,
@@ -822,6 +823,25 @@ maxU32 : U32
 ## and zero is the lowest unsigned number. Unsigned numbers cannot be negative.
 minU32 : U32
 
+## The highest number that can be stored in an #I128 without overflowing its
+## available memory and crashing.
+##
+## For reference, this number is `170_141_183_460_469_231_731_687_303_715_884_105_727`,
+## which is over 2 million.
+##
+## Note that this is smaller than the positive version of #Int.minI128,
+## which means if you call #Num.abs on #Int.minI128, it will overflow and crash!
+maxI128 : I128
+
+## The min number that can be stored in an #I128 without underflowing its
+## available memory and crashing.
+##
+## For reference, this number is `-170_141_183_460_469_231_731_687_303_715_884_105_728`.
+##
+## Note that the positive version of this number is larger than #Int.maxI128,
+## which means if you call #Num.abs on #Int.minI128, it will overflow and crash!
+minI128 : I128
+
 ## The highest supported #F64 value you can have, which is approximately 1.8 × 10^308.
 ##
 ## If you go higher than this, your running Roc code will crash - so be careful not to!

compiler/builtins/src/std.rs

@@ -397,6 +397,9 @@ pub fn types() -> MutMap<Symbol, (SolvedType, Region)> {
         Box::new(bool_type()),
     );
 
+    // minI128 : I128
+    add_type!(Symbol::NUM_MIN_I128, i128_type());
+
     // maxI128 : I128
     add_type!(Symbol::NUM_MAX_I128, i128_type());