PCASTL: by Parent and Childset Accessible Syntax Tree Language

The "parent" keyword to access a parent node in the code syntax tree.
The "childset" keyword to access a child node in the code syntax tree.
The use of explicit code segments delimited with ` and '.
Allows calls to dynamic-link libraries, shared object libraries or dynamic libraries.
Object, array and chained list data types. They are respectively created by internal functions names, array and list.
ANSI stdio.h interface for single-byte strings functions.
Turing complete.

The most recent version is 3.5 and was released on 2018-03-31.
List of changes.

So, what's a syntax tree?

For example, inside the interpreter, the tree having its root in the variable fact after the following code has been executed:

fact = function(x)
{
   if (x == 1) return(1)
   return(x * fact(x - 1))
}

is:

Syntax Tree

Below you can see how childset and parent keywords can be used to navigate this tree.

> info(fact)
[node_type]     "function definition"
[nb_children]   2
[parameters][0] "x"
>
> info(fact.childset[0])
[node_type]     "list"
[nb_children]   1
>
> info(fact.childset[0].childset[0])
[node_type]     "variable"
[nb_children]   0
[name]  "x"
>
> info(fact.childset[1])
[node_type]     "list"
[nb_children]   2
>
> info(fact.childset[1].childset[0])
[node_type]     "if statement"
[nb_children]   2
>
> info(fact.childset[1].childset[1])
[node_type]     "function call"
[nb_children]   2
[nb_args]       1
>
> info(fact.childset[0].parent)
[node_type]     "function definition"
[nb_children]   2
[parameters][0] "x"

Here are ways to edit the tree:

> mknode(fact.childset[1], `if (x < 1) {
+    print("Parameter must be greater than zero.")
+    abort()
+ }', 0)
> fact(-2)
        "Parameter must be greater than zero."
> info(fact.childset[1])
[node_type]     "list"
[nb_children]   3
>
> info(fact.childset[1].childset[0].childset[1].childset[1])
[node_type]     "function call"
[nb_children]   2
[nb_args]       0
>
> fact.childset[1].childset[0].childset[1].childset[1] = `return(-1)'
        0x431c20
> info(fact.childset[1].childset[0].childset[1].childset[1])
[node_type]     "function call"
[nb_children]   2
[nb_args]       1
>
> fact(-2)
        "Parameter must be greater than zero."
        -1