Add seq function (#205)

* Add seq function for generating a sequence of numbers

* Use untilStep to build the seq command response

docs/integer_slice.md

@@ -23,3 +23,19 @@ untilStep 3 6 2
 
 The above will produce `[3 5]` by starting with 3, and adding 2 until it is equal
 or greater than 6. This is similar to Python's `range` function.
+
+## seq
+
+Works like the bash `seq` command.
+* 1 parameter  (end) - will generate all counting integers between 1 and `end` inclusive.
+* 2 parameters (start, end) - will generate all counting integers between `start` and `end` inclusive incrementing or decrementing by 1.
+* 3 parameters (start, step, end) - will generate all counting integers between `start` and `end` inclusive incrementing or decrementing by `step`.
+
+```
+seq 5       => 0 1 2 3 4 5
+seq -3      => 1 0 -1 -2 -3
+seq 0 2     => 0 1 2
+seq 2 -2    => 2 1 0 -1 -2
+seq 0 2 10  => 0 2 4 6 8 10
+seq 0 -2 -5 => 0 -2 -4
+```

functions.go

@@ -163,6 +163,7 @@ var genericMap = map[string]interface{}{
 	"int64":     toInt64,
 	"int":       toInt,
 	"float64":   toFloat64,
+	"seq":       seq,
 	"toDecimal": toDecimal,
 
 	//"gt": func(a, b int) bool {return a > b},

numeric.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"math"
 	"strconv"
+	"strings"
 
 	"github.com/spf13/cast"
 )
@@ -112,3 +113,43 @@ func toDecimal(v interface{}) int64 {
 	}
 	return result
 }
+
+func seq(params ...int) string {
+	increment := 1
+	switch len(params) {
+	case 0:
+		return ""
+	case 1:
+		start := 1
+		end := params[0]
+		if end < start {
+			increment = -1
+		}
+		return intArrayToString(untilStep(start, end+increment, increment), " ")
+	case 3:
+		start := params[0]
+		end := params[2]
+		step := params[1]
+		if end < start {
+			increment = -1
+			if step > 0 {
+				return ""
+			}
+		}
+		return intArrayToString(untilStep(start, end+increment, step), " ")
+	case 2:
+		start := params[0]
+		end := params[1]
+		step := 1
+		if end < start {
+			step = -1
+		}
+		return intArrayToString(untilStep(start, end+step, step), " ")
+	default:
+		return ""
+	}
+}
+
+func intArrayToString(slice []int, delimeter string) string {
+	return strings.Trim(strings.Join(strings.Fields(fmt.Sprint(slice)), delimeter), "[]")
+}

numeric_test.go

@@ -219,3 +219,24 @@ func TestRound(t *testing.T) {
 	assert.Equal(t, 123.23, round(123.2329999, 2, .3))
 	assert.Equal(t, 123.24, round(123.233, 2, .3))
 }
+
+func TestSeq(t *testing.T) {
+	tests := map[string]string{
+		`{{seq 0 1 3}}`:   "0 1 2 3",
+		`{{seq 0 3 10}}`:  "0 3 6 9",
+		`{{seq 3 3 2}}`:   "",
+		`{{seq 3 -3 2}}`:  "3",
+		`{{seq}}`:         "",
+		`{{seq 0 4}}`:     "0 1 2 3 4",
+		`{{seq 5}}`:       "1 2 3 4 5",
+		`{{seq -5}}`:      "1 0 -1 -2 -3 -4 -5",
+		`{{seq 0}}`:       "1 0",
+		`{{seq 0 1 2 3}}`: "",
+		`{{seq 0 -4}}`:    "0 -1 -2 -3 -4",
+	}
+	for tpl, expect := range tests {
+		if err := runt(tpl, expect); err != nil {
+			t.Error(err)
+		}
+	}
+}