Merge branch '1.6.x'

CONTRIBUTING.md

@@ -8,7 +8,7 @@ repository.
 
 Since we follow [semver](https://semver.org/),
 when a new feature is released we don't backport it but simply
-create a new version branch, such as `1.5.x`. Bugs, instead,
+create a new version branch, such as `1.6.x`. Bugs, instead,
 might be backported from `1.1.0` to, for example, `1.0.x` and we
 will have a new [release](https://github.com/abs-lang/abs/releases),
 say `1.0.1` for the `1.0.x` version branch.

README.md

@@ -24,12 +24,12 @@
 
 # The ABS programming language
 
-ABS is a scripting language that works best when you're scripting on
+ABS is a programming language that works best when you're scripting on
 your terminal. It tries to combine the elegance of languages
 such as Python, or Ruby, to the convenience of Bash.
 
 ``` bash
-tz = $(cat /etc/timezone);
+tz = `cat /etc/timezone`
 continent, city = tz.split("/")
 
 echo("Best city in the world?")
@@ -73,7 +73,7 @@ And here's how you could write the same code in ABS:
 
 ``` bash
 # Simple program that fetches your IP and sums it up
-res = $(curl -s 'https://api.ipify.org?format=json');
+res = `curl -s 'https://api.ipify.org?format=json'`
 
 if !res.ok {
   echo("An error occurred: %s", res)

ast/ast.go

@@ -492,10 +492,18 @@ func (al *ArrayLiteral) String() string {
 	return out.String()
 }
 
+// IndexExpression allows accessing a single index, or a range,
+// over a string or an array.
+//
+// array[1:10]	-> left[index:end]
+// array[1] 	-> left[index]
+// string[1] 	-> left[index]
 type IndexExpression struct {
-	Token token.Token // The [ token
-	Left  Expression
-	Index Expression
+	Token   token.Token // The [ token
+	Left    Expression  // the argument on which the index is access eg array of array[1]
+	Index   Expression  // the left-most index eg. 1 in array[1] or array[1:10]
+	IsRange bool        // whether the expression is a range (1:10)
+	End     Expression  // the end of the range, if the expression is a range
 }
 
 func (ie *IndexExpression) expressionNode()      {}
@@ -506,7 +514,13 @@ func (ie *IndexExpression) String() string {
 	out.WriteString("(")
 	out.WriteString(ie.Left.String())
 	out.WriteString("[")
-	out.WriteString(ie.Index.String())
+
+	if ie.IsRange {
+		out.WriteString(ie.Index.String() + ":" + ie.End.String())
+	} else {
+		out.WriteString(ie.Index.String())
+	}
+
 	out.WriteString("])")
 
 	return out.String()

docs/README.md

@@ -21,12 +21,12 @@
   <img href="https://github.com/abs-lang/abs" alt="undefined" src="https://img.shields.io/github/stars/abs-lang/abs.svg?style=social">
 </p>
 
-ABS is a scripting language that works best when you're scripting on
+ABS is a programming language that works best when you're scripting on
 your terminal. It tries to combine the elegance of languages
 such as Python, or Ruby, to the convenience of Bash.
 
 ``` bash
-tz = $(cat /etc/timezone);
+tz = `cat /etc/timezone`;
 continent, city = tz.split("/")
 
 echo("Best city in the world?")
@@ -48,14 +48,14 @@ in Bash:
 
 ``` bash
 # Simple program that fetches your IP and sums it up
-RES=$(curl -s 'https://api.ipify.org?format=json' || "ERR")
+RES=`curl -s 'https://api.ipify.org?format=json' || "ERR"`
 
 if [ "$RES" = "ERR" ]; then
     echo "An error occurred"
     exit 1
 fi
 
-IP=$(echo $RES | jq -r ".ip")
+IP=`echo $RES | jq -r ".ip"`
 IFS=. read first second third fourth <<EOF
 ${IP##*-}
 EOF
@@ -70,7 +70,7 @@ And here's how you could write the same code in ABS:
 
 ``` bash
 # Simple program that fetches your IP and sums it up
-res = $(curl -s 'https://api.ipify.org?format=json');
+res = `curl -s 'https://api.ipify.org?format=json'`
 
 if !res.ok {
   echo("An error occurred: %s", res)

docs/installer.sh

@@ -27,7 +27,7 @@ if [ "${MACHINE_TYPE}" = 'x86_64' ]; then
   ARCH="amd64"
 fi
 
-VERSION=1.5.1
+VERSION=1.6.0
 
 echo "Trying to detect the details of your architecture."
 echo ""

docs/introduction/how-to-run-abs-code.md

@@ -61,7 +61,7 @@ the fly:
 $ abs
 Hello there, welcome to the ABS programming language!
 Type 'quit' when you're done, 'help' if you get lost!
-⧐  ip = $(curl icanhazip.com)
+⧐  ip = `curl icanhazip.com`
 ⧐  ip.ok
 true
 ⧐  ip()

docs/introduction/why-another-scripting-language.md

@@ -44,7 +44,7 @@ call the API of nba.com in order to retrieve the stats for
 one of last year's NBA games:
 
 ``` bash
-r = $(curl "http://data.nba.net/prod/v1/20170201/0021600732_boxscore.json" -H 'DNT: 1' -H 'Accept-Encoding: gzip, deflate, sdch' -H 'Accept-Language: en' -H 'User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/57.0.2987.133 Safari/537.36' -H 'Accept: */*' -H 'Referer: http://stats.nba.com/' -H 'Connection: keep-alive' --compressed);
+r = `curl "http://data.nba.net/prod/v1/20170201/0021600732_boxscore.json" -H 'DNT: 1' -H 'Accept-Encoding: gzip, deflate, sdch' -H 'Accept-Language: en' -H 'User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/57.0.2987.133 Safari/537.36' -H 'Accept: */*' -H 'Referer: http://stats.nba.com/' -H 'Connection: keep-alive' --compressed`;
 
 if !r.ok {
     echo("Could not fetch game data. Bummer!")
@@ -79,7 +79,7 @@ A sneak-peek at some of the things ABS can elegantly do:
 
 ``` bash
 # Unix pipes work
-ip = $(curl icanhazip.com | tr -d '\n')
+ip = `curl icanhazip.com | tr -d '\n'`
 
 # We now have a string -> "10.10.10.12"
 echo(ip)

docs/misc/error.md

@@ -21,10 +21,10 @@ $ cat examples/error-parse.abs
 m.a = 'abc'
 
 # this is a command terminated with a semi
-d/d = $(command);
+d/d = `command`;
 
 # this is a command terminated with a LF
-c/c = $(command)
+c/c = `command`
 
 # this is a bad infix operator
 b %% c
@@ -34,9 +34,9 @@ $ abs examples/error-parse.abs
 	no prefix parse function for '=' found
 	[4:5]	m.a = 'abc'
 	no prefix parse function for '=' found
-	[7:5]	d/d = $(command);
+	[7:5]	d/d = `command`;
 	no prefix parse function for '=' found
-	[10:5]	c/c = $(command)
+	[10:5]	c/c = `command`
 	no prefix parse function for '%' found
 	[13:4]	b %% c
 

docs/misc/technical-details.md

@@ -37,9 +37,9 @@ tests/test-parser.abs
 	no prefix parse function for '=' found
 	[4:5]	m.a = 'abc'
 	no prefix parse function for '=' found
-	[7:5]	d/d = $(command);
+	[7:5]	d/d = `command`;
 	no prefix parse function for '=' found
-	[10:5]	c/c = $(command)
+	[10:5]	c/c = `command`
 	no prefix parse function for '%' found
 	[13:4]	b %% c
 	no prefix parse function for '&&' found
@@ -205,7 +205,7 @@ ERROR: type mismatch: NULL + NUMBER
 
 ## Roadmap
 
-We're currently working on [1.6](https://github.com/abs-lang/abs/milestone/13).
+We're currently working on [1.7](https://github.com/abs-lang/abs/milestone/14).
 
 ## Next
 

docs/syntax/return.md

@@ -20,6 +20,14 @@ func = f(x) {
 func(9) # 10
 ```
 
+The default value of a `return` is `null`:
+
+```
+if x {
+    return # null
+}
+```
+
 ## Next
 
 That's about it for this section!

docs/syntax/system-commands.md

@@ -4,11 +4,10 @@ Executing system commands is one of the most important features
 of ABS, as it allows the mixing of conveniency of the shell with
 the syntax of a modern programming language.
 
-Commands are executed either with `$(command)` or `` `command` ``,
+Commands are executed with the `` `command` `` syntax,
 which resemble Bash's syntax to execute commands in a subshell:
 
 ``` bash
-date = $(date) # "Sun Apr 1 04:30:59 +01 1995"
 date = `date` # "Sun Apr 1 04:30:59 +01 1995"
 ```
 
@@ -18,7 +17,7 @@ encounter an error, the same string would hold the error
 message:
 
 ``` bash
-date = $(dat) # "bash: dat: command not found"
+date = `dat` # "bash: dat: command not found"
 ```
 
 It would be fairly painful to have to parse strings
@@ -27,60 +26,11 @@ in ABS, the returned string has a special property `ok` that
 checks whether the command was successful:
 
 ``` bash
-ls = $(ls -la)
-
-if ls.ok {
-    echo("hello world")
-}
-
-# or
-
 if `ls -la`.ok {
     echo("hello world")
 }
 ```
-It is also possible to execute a shell command without capturing its
-input or output using the `exec(command)` function. This allows long running
-or interactive programs to be run using the terminal's Standard IO
-(stdin, stdout, stderr). For example:
-```bash
-exec("sudo visudo")
-```
-would open the default text editor in super user mode on the /etc/sudoers file.
 
-Unlike the normal backtick command execution syntax above,
-the `exec(command)` function call does not return a result string unless it fails. 
-Therefore, the `exec(command)` may be the last command executed in a script
-file leaving the executed command in charge of the terminal IO until it
-terminates.  
-
-For example, an ABS script might be used to marshall the command line args
-for an interactive program such as the nano editor:
-
-``` bash
-$ cat abs/tests/test-exec.abs
-# marshall the args for the nano editor
-# if the filename is not given in the args, prompt for it
-# if the file is located outside the user's home dir, invoke sudo nano filename
-
-cmd = 'nano'
-filename = arg(2)
-homedir = env("HOME")
-
-while filename == '' {
-    echo("Please enter file name for %s: ", cmd)
-    filename = stdin()
-}
-
-if filename.prefix('~/') || filename.prefix(homedir) {
-    sudo = ''
-} else {
-    sudo = 'sudo'
-}
-
-# execute the command with live stdIO
-exec("$sudo $cmd $filename")
-```
 ## Executing commands in background
 
 Sometimes you might want to execute a command in
@@ -155,13 +105,21 @@ and if you need `$` literals in your command, you
 simply need to escape them with a `\`:
 
 ``` bash
-$(echo $PWD) # "" since the ABS variable PWD doesn't exist
-$(echo \$PWD) # "/go/src/github.com/abs-lang/abs"
+`echo $PWD` # "" since the ABS variable PWD doesn't exist
+`echo \$PWD` # "/go/src/github.com/abs-lang/abs"
 ```
 
-## Limitations
+## Alternative $() syntax
+
+Even though the use of backticks is the standard recommended
+way to run system commands, for the ease of embedding ABS also
+allows you to use the `$(command)` syntax:
+
+```
+$(basename $(dirname "/tmp/make/life/easy")) // "easy"
+```
 
-Currently, commands that use the `$()` syntax need to be
+Commands that use the `$()` syntax need to be
 on their own line, meaning that you will not
 be able to have additional code on the same line.
 This will throw an error:
@@ -170,10 +128,56 @@ This will throw an error:
 $(sleep 10); echo("hello world")
 ```
 
-Note that this is currently a limitation that will likely
-be removed in the future (see [#41](https://github.com/abs-lang/abs/issues/41)).
+## Executing commands without capturing I/O
+
+It is also possible to execute a shell command without capturing its
+input or output using the `exec(command)` function. This allows long running
+or interactive programs to be run using the terminal's Standard IO
+(stdin, stdout, stderr). For example:
+
+```bash
+exec("sudo visudo")
+```
+
+would open the default text editor in super user mode on the /etc/sudoers file.
+
+Unlike the normal backtick command execution syntax above,
+the `exec(command)` function call does not return a result string unless it fails. 
+Therefore, the `exec(command)` may be the last command executed in a script
+file leaving the executed command in charge of the terminal IO until it
+terminates.  
+
+For example, an ABS script might be used to marshall the command line args
+for an interactive program such as the nano editor:
+
+``` bash
+$ cat abs/tests/test-exec.abs
+# marshall the args for the nano editor
+# if the filename is not given in the args, prompt for it
+# if the file is located outside the user's home dir, invoke sudo nano filename
+
+cmd = 'nano'
+filename = arg(2)
+homedir = env("HOME")
+
+while filename == '' {
+    echo("Please enter file name for %s: ", cmd)
+    filename = stdin()
+}
+
+if filename.prefix('~/') || filename.prefix(homedir) {
+    sudo = ''
+} else {
+    sudo = 'sudo'
+}
+
+# execute the command with live stdIO
+exec("$sudo $cmd $filename")
+```
+
+## Limitations
 
-Also note that, currently, the implementation of system commands
+Note that the implementation of system commands
 requires the `bash` executable to [be available on the system](https://github.com/abs-lang/abs/blob/5b5b0abf3115a5dd4dfe8485501f8765985ad0db/evaluator/evaluator.go#L696-L722).
 On Windows, commands are executed through [cmd.exe](https://github.com/abs-lang/abs/blob/ee793641be09ad8572c3e913fef8468f69b0c0a2/evaluator/evaluator.go#L1101-L1103).
 Future work will make it possible to select which shell to use,