Math operators (#1601)

* Add some math operations

* WIP for adding compound expressions

* precedence parsing

* paren expressions

* better lhs handling

* add compound comparisons and shorthand lefthand parsing

* Add or comparison and shorthand paths

crates/nu-protocol/src/value/primitive.rs

@@ -41,7 +41,7 @@ pub enum Primitive {
     /// A date value, in UTC
     Date(DateTime<Utc>),
     /// A count in the number of seconds
-    Duration(u64),
+    Duration(i64),
     /// A range of values
     Range(Box<Range>),
     /// A file path
@@ -276,7 +276,7 @@ pub fn format_primitive(primitive: &Primitive, field_name: Option<&String>) -> S
 }
 
 /// Format a duration in seconds into a string
-pub fn format_duration(sec: u64) -> String {
+pub fn format_duration(sec: i64) -> String {
     let (minutes, seconds) = (sec / 60, sec % 60);
     let (hours, minutes) = (minutes / 60, minutes % 60);
     let (days, hours) = (hours / 24, hours % 24);
@@ -290,13 +290,73 @@ pub fn format_duration(sec: u64) -> String {
     }
 }
 
+#[allow(clippy::cognitive_complexity)]
 /// Format a UTC date value into a humanized string (eg "1 week ago" instead of a formal date string)
 pub fn format_date(d: &DateTime<Utc>) -> String {
     let utc: DateTime<Utc> = Utc::now();
 
     let duration = utc.signed_duration_since(*d);
 
-    if duration.num_weeks() >= 52 {
+    if duration.num_seconds() < 0 {
+        // Our duration is negative, so we need to speak about the future
+        if -duration.num_weeks() >= 52 {
+            let num_years = -duration.num_weeks() / 52;
+
+            format!(
+                "{} year{} from now",
+                num_years,
+                if num_years == 1 { "" } else { "s" }
+            )
+        } else if -duration.num_weeks() >= 4 {
+            let num_months = -duration.num_weeks() / 4;
+
+            format!(
+                "{} month{} from now",
+                num_months,
+                if num_months == 1 { "" } else { "s" }
+            )
+        } else if -duration.num_weeks() >= 1 {
+            let num_weeks = -duration.num_weeks();
+
+            format!(
+                "{} week{} from now",
+                num_weeks,
+                if num_weeks == 1 { "" } else { "s" }
+            )
+        } else if -duration.num_days() >= 1 {
+            let num_days = -duration.num_days();
+
+            format!(
+                "{} day{} from now",
+                num_days,
+                if num_days == 1 { "" } else { "s" }
+            )
+        } else if -duration.num_hours() >= 1 {
+            let num_hours = -duration.num_hours();
+
+            format!(
+                "{} hour{} from now",
+                num_hours,
+                if num_hours == 1 { "" } else { "s" }
+            )
+        } else if -duration.num_minutes() >= 1 {
+            let num_minutes = -duration.num_minutes();
+
+            format!(
+                "{} min{} from now",
+                num_minutes,
+                if num_minutes == 1 { "" } else { "s" }
+            )
+        } else {
+            let num_seconds = -duration.num_seconds();
+
+            format!(
+                "{} sec{} from now",
+                num_seconds,
+                if num_seconds == 1 { "" } else { "s" }
+            )
+        }
+    } else if duration.num_weeks() >= 52 {
         let num_years = duration.num_weeks() / 52;
 
         format!(