An experimental Nit interactive interpreter

This tool is outside src/ because:

1. Is is greatly experimental
2. It can depend on readline (GPL3) whereas the rest of nitc is Apache2. Both are compatible but the final binary result is GLP3.

Features

• use GNU readline to read lines
• use importation/refinement to handle incremental execution (so basically everything works out of the box)
• maintain an interpreter and live objects (the model grows but the interpreter and runtime data are reused)
• runtime errors/aborts return to the interactive loop
• top-level variables are preserved but are only visible at the top level
• Basic FFI

Main missing feature

• No model/object inspection

Examples

--> is the prompt, ... the continuation prompt. What follows is the user input. The rest is the output.

Basic instructions

$ nitin
--> print 5+2
7
--> var a = 5
--> print a + 3
8

Complex and control statements

-->var sum=0
-->for i in [0..5[ do
...print i
...sum += i
...end
0
1
2
3
4
-->print sum
10

You can use do blocks to delay the execution and control the scope of variables.

-->do
...var sum=0
...for i in [0..50[ do
...sum += i
...end
...print sum
...end
1225

Classes and methods

-->class A
...fun foo do
...print "hello"
...end
...end
-->(new A).foo
hello

Error management

In case of static errors, the history (up arrow) can be reused and updated.

-->class
...end
    end
    ^: Syntax Error: unexpected keyword 'end'.
-->class A   **up arrow and update, thanks readline**
end
1,7: Redef Error: `A` is an imported class. Add the `redef` keyword to refine it.
    class A
          ^
-->redef class A **up arrow and update again, thanks readline**
redef fun foo do print "Bye"
end
-->(new A).foo
bye

Class refinement

Class refinement is available

-->redef class String
...fun foo: String do return self + "foo"
...end
-->print "hello".foo
hellofoo

Top-level methods automatically refine Sys.

-->foo
1,1--3: Error: method or variable `foo` unknown in `Sys`.
    foo
    ^
-->fun foo do
...print "I'm sys"
...end
-->foo
I'm sys

Already instantiated objects gain the new methods, attributes and specializations.

-->class A
...end
-->var a = new A
-->print a
--><A:#561daea16660>
-->redef class A
...redef fun to_s do return "A"
...end
-->print a
A

However, the new attributes are left uninitialized (default values or init are not recomputed on existing objects)

-->redef class A
...var v = "foo"
...redef fun to_s do return "A:{v}"
...end
--->print a
Runtime error: Uninitialized attribute _v
    redef fun to_s do return "A:{v}"
                                 ^
,---- Stack trace -- - -  -
| input-6$A$to_s (13,30)
| file$Sys$print (lib/core/file.nit:1694,19--29)
| input-7$Sys$main (15,1--7)
`------------------- - -  -
-->a.v = "bar"
-->print a
A:bar

Dynamic importation

-->print([0..10[.to_a.to_json)
1,20--26: Error: method `to_json` does not exists in `Array[Int]`.
    print([0..10[.to_a.to_json)
                       ^
-->import json
-->print([0..10[.to_a.to_json)
[0,1,2,3,4,5,6,7,8,9]

FFI

The FFI is handled as with the non-interactive interpreter.

-->fun hello `{
...puts("Hello, world");
...`}
-->hello
Hello, world