Human-readable time durations

examples/datetime_human_tests.nbt

@@ -0,0 +1,38 @@
+assert((0 second         // human) == "0 seconds")
+assert((1 second         // human) == "1 second")
+assert((5 second         // human) == "5 seconds")
+assert((1.5 second       // human) == "1.500 seconds")
+
+assert((60 seconds       // human) == "1 minute")
+assert((73 seconds       // human) == "1 minute + 13 seconds")
+assert((120 seconds      // human) == "2 minutes")
+assert((60.1 seconds     // human) == "1 minute + 0.100 seconds")
+assert((1 minute         // human) == "1 minute")
+assert((1.25 minute      // human) == "1 minute + 15 seconds")
+assert((2.5 minute       // human) == "2 minutes + 30 seconds")
+
+assert((1 hour           // human) == "1 hour")
+assert((1.5 hour         // human) == "1 hour + 30 minutes")
+assert((2 hour           // human) == "2 hours")
+assert((1 hour + 1 sec   // human) == "1 hour + 1 second")
+
+assert((1 day            // human) == "1 day")
+assert((1.37 day         // human) == "1 day + 8 hours + 52 minutes + 48 seconds")
+
+assert((1 week           // human) == "7 days")
+assert((1.5 weeks        // human) == "10 days + 12 hours")
+assert((2 weeks          // human) == "14 days")
+
+assert((1 sidereal_day   // human) == "23 hours + 56 minutes + 4.090500 seconds")
+
+assert((10000 days       // human) == "10000 days")
+assert((50 million days  // human) == "50_000_000 days")
+
+assert((1e12 days        // human) == "1_000_000_000_000 days")
+assert((1e15 days        // human) == "1.0e+15 days")
+
+assert((1 ms             // human) == "0.001 seconds")
+assert((1 µs             // human) == "0.000001 seconds")
+assert((1 ns             // human) == "0.000000001 seconds")
+assert((1234 ns          // human) == "0.000001234 seconds")
+assert((1s + 1234 ns     // human) == "1.000001234 seconds")

numbat/modules/datetime/human.nbt

@@ -0,0 +1,36 @@
+use core::functions
+use core::strings
+use units::si
+use datetime::functions
+
+fn _human_num_days(time: Time) -> Scalar = floor(time / day)
+
+fn _human_join(a: String, b: String) -> String =
+  if str_slice(a, 0, 2) == "0 " then b else if str_slice(b, 0, 2) == "0 " then a else "{a} + {b}"
+
+fn _remove_plural_suffix(str: String) -> String =
+  if str_slice(str, 0, 2) == "1 " then str_slice(str, 0, str_length(str) - 1) else str
+
+fn _human_seconds(dt: DateTime) -> String =
+  _remove_plural_suffix(format_datetime("%-S%.f seconds", dt))
+
+fn _human_minutes(dt: DateTime) -> String =
+  _remove_plural_suffix(format_datetime("%-M minutes", dt))
+
+fn _human_hours(dt: DateTime) -> String =
+  _remove_plural_suffix(format_datetime("%-H hours", dt))
+
+fn _human_days(num_days: Scalar) -> String =
+  _remove_plural_suffix("{num_days} days")
+
+fn _human_readable_duration(time: Time, dt: DateTime, num_days: Scalar) -> String =
+    _human_join(_human_join(_human_join(_human_days(_human_num_days(time)), _human_hours(dt)), _human_minutes(dt)), _human_seconds(dt))
+
+# Implementation details:
+# we skip hours/minutes/seconds for durations larger than 1000 days because:
+#   (a) we run into floating point precision problems at the nanosecond level at this point
+#   (b) for much larger numbers, we can't convert to DateTimes anymore
+fn human(time: Time) =
+  if _human_num_days(time) > 1000
+    then "{_human_num_days(time)} days" 
+    else _human_readable_duration(time, parse_datetime("0001-01-01T00:00:00Z") + time, _human_num_days(time))

numbat/modules/prelude.nbt

@@ -30,3 +30,4 @@ use physics::constants
 use physics::temperature_conversion
 
 use datetime::functions
+use datetime::human

numbat/src/bytecode_interpreter.rs

@@ -130,8 +130,8 @@ impl BytecodeInterpreter {
                     Op::DiffDateTime
                 } else {
                     match operator {
-                        BinaryOperator::Add => Op::AddDateTime,
-                        BinaryOperator::Sub => Op::SubDateTime,
+                        BinaryOperator::Add => Op::AddToDateTime,
+                        BinaryOperator::Sub => Op::SubFromDateTime,
                         BinaryOperator::ConvertTo => Op::ConvertDateTime,
                         _ => unreachable!("{operator:?} is not valid with a DateTime"), // should be unreachable, because the typechecker will error first
                     }

numbat/src/interpreter.rs

@@ -41,6 +41,10 @@ pub enum RuntimeError {
     DateParsingError(chrono::ParseError),
     #[error("Unknown timezone: {0}")]
     UnknownTimezone(String),
+    #[error("Exceeded maximum size for time durations")]
+    DurationOutOfRange,
+    #[error("DateTime out of range")]
+    DateTimeOutOfRange,
 }
 
 #[derive(Debug, PartialEq, Eq)]

numbat/src/vm.rs

@@ -73,9 +73,9 @@ pub enum Op {
     LogicalNeg,
 
     /// Similar to Add, but has DateTime on the LHS and a quantity on the RHS
-    AddDateTime,
+    AddToDateTime,
     /// Similar to Sub, but has DateTime on the LHS and a quantity on the RHS
-    SubDateTime,
+    SubFromDateTime,
     /// Computes the difference between two DateTimes
     DiffDateTime,
     /// Converts a DateTime value to another timezone
@@ -122,9 +122,9 @@ impl Op {
             Op::Negate
             | Op::Factorial
             | Op::Add
-            | Op::AddDateTime
+            | Op::AddToDateTime
             | Op::Subtract
-            | Op::SubDateTime
+            | Op::SubFromDateTime
             | Op::DiffDateTime
             | Op::ConvertDateTime
             | Op::Multiply
@@ -157,9 +157,9 @@ impl Op {
             Op::Negate => "Negate",
             Op::Factorial => "Factorial",
             Op::Add => "Add",
-            Op::AddDateTime => "AddDateTime",
+            Op::AddToDateTime => "AddDateTime",
             Op::Subtract => "Subtract",
-            Op::SubDateTime => "SubDateTime",
+            Op::SubFromDateTime => "SubDateTime",
             Op::DiffDateTime => "DiffDateTime",
             Op::ConvertDateTime => "ConvertDateTime",
             Op::Multiply => "Multiply",
@@ -649,23 +649,28 @@ impl Vm {
                     };
                     self.push_quantity(result.map_err(RuntimeError::QuantityError)?);
                 }
-                op @ (Op::AddDateTime | Op::SubDateTime) => {
+                op @ (Op::AddToDateTime | Op::SubFromDateTime) => {
                     let rhs = self.pop_quantity();
                     let lhs = self.pop_datetime();
 
                     // for time, the base unit is in seconds
                     let base = rhs.to_base_unit_representation();
                     let seconds_f = base.unsafe_value().to_f64();
 
-                    let duration = chrono::Duration::seconds(seconds_f.trunc() as i64)
+                    let duration = chrono::Duration::try_seconds(seconds_f.trunc() as i64)
+                        .ok_or(RuntimeError::DurationOutOfRange)?
                         + chrono::Duration::nanoseconds(
                             (seconds_f.fract() * 1_000_000_000f64).round() as i64,
                         );
 
                     self.push(Value::DateTime(
                         match op {
-                            Op::AddDateTime => lhs + duration,
-                            Op::SubDateTime => lhs - duration,
+                            Op::AddToDateTime => lhs
+                                .checked_add_signed(duration)
+                                .ok_or(RuntimeError::DateTimeOutOfRange)?,
+                            Op::SubFromDateTime => lhs
+                                .checked_sub_signed(duration)
+                                .ok_or(RuntimeError::DateTimeOutOfRange)?,
                             _ => unreachable!(),
                         },
                         chrono::Local::now().offset().fix(),