add expr-lang.org support (use with -e)

pkg/runexpr/run.go

@@ -0,0 +1,63 @@
+package runexpr
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/expr-lang/expr"
+)
+
+type Env struct {
+	Now                                  func() time.Time
+	Dur, D                               func(string) time.Duration
+	Strf                                 func(any, ...any) string
+	Diff                                 func(a, b time.Time) time.Duration
+	Add                                  func(time.Time, time.Duration) time.Time
+	Time, T                              func(string, ...string) time.Time
+	Human                                func(time.Duration) string
+	Years, Days, Hours, Minutes, Seconds func(time.Duration) float64
+	Clock                                func(time.Time) string
+	Unix                                 func(time.Time) int64
+	TZ                                   func(time.Time, any) time.Time
+}
+
+func RunExpr(code string) {
+	env := Env{
+		Now:     time.Now,
+		Dur:     parseDuration,
+		D:       parseDuration,
+		Strf:    strfTime,
+		Diff:    timeDiff,
+		Add:     timeAdd,
+		Time:    newTime,
+		T:       newTime,
+		Human:   formatDuration,
+		Years:   toYears,
+		Days:    toDays,
+		Hours:   toHours,
+		Minutes: toMinutes,
+		Seconds: toSeconds,
+		Clock:   toClock,
+		Unix:    toUnix,
+		TZ:      toTZ,
+	}
+
+	options := []expr.Option{
+		expr.Env(Env{}),
+		expr.Operator("-", "Diff"), // custom operator to diff two time.Time's
+		expr.Operator("+", "Add"),  // custom operator to add time.Duration to a time.Time
+	}
+
+	program, err := expr.Compile(code, options...)
+	if err != nil {
+		fmt.Printf("%v", err)
+		return
+	}
+
+	output, err := expr.Run(program, env)
+	if err != nil {
+		panic(err)
+	}
+
+	fmt.Println(output)
+}