added sleep function, closes #157

docs/types/builtin-function.md

@@ -166,6 +166,14 @@ Type 'quit' when you're done, 'help' if you get lost!
 STRING
 ```
 
+### sleep(ms)
+
+Halts the process for as many `ms` you specified:
+
+``` bash
+sleep(1000) # sleeps for 1 second
+```
+
 ## Next
 
 That's about it for this section!

evaluator/evaluator_test.go

@@ -776,6 +776,7 @@ c")`, []string{"a", "b", "c"}},
 		{`"A great movie".upper()`, "A GREAT MOVIE"},
 		{`"  A great movie  ".trim()`, "A great movie"},
 		{`"  A great movie  ".trim_by(" A")`, "great movie"},
+		{`sleep(1000)`, nil},
 	}
 	for _, tt := range tests {
 		evaluated := testEval(tt.input)

evaluator/functions.go

@@ -9,6 +9,7 @@ import (
 	"sort"
 	"strconv"
 	"strings"
+	"time"
 
 	"github.com/abs-lang/abs/ast"
 	"github.com/abs-lang/abs/lexer"
@@ -271,6 +272,11 @@ func getFns() map[string]*object.Builtin {
 			Types: []string{object.ARRAY_OBJ},
 			Fn:    joinFn,
 		},
+		// sleep(3000)
+		"sleep": &object.Builtin{
+			Types: []string{object.NUMBER_OBJ},
+			Fn:    sleepFn,
+		},
 	}
 }
 
@@ -1269,3 +1275,15 @@ func joinFn(args ...object.Object) object.Object {
 
 	return &object.String{Token: tok, Value: strings.Join(newElements, args[1].(*object.String).Value)}
 }
+
+func sleepFn(args ...object.Object) object.Object {
+	err := validateArgs("sleep", args, 1, [][]string{{object.NUMBER_OBJ}})
+	if err != nil {
+		return err
+	}
+
+	ms := args[0].(*object.Number)
+	time.Sleep(time.Duration(ms.Value) * time.Millisecond)
+
+	return NULL
+}