#afos basic

In BASIC when you press enter, it usually denotes the end of a code statement. What that means is that the interpreter can take what you just typed and convert it into tokens and execute it on the fly.

That is fine and dandy for small one line expressions but what about complex constructs like loops and functions. Its hard to go back and edit mistakes. The original BASIC was designed to work with line numbers. We had the ability to overwrite line numbers to fix mistakes. Things have changed since then. Line numbers are obsolete. FreeBASIC is a compiler and its not interactive. Hence they didn't have to worry about that stuff. Personally, I do like the ability to do interactive development. What Microsoft did in Q'BASIC is, they had a text editor on top and an interactive command prompt at the bottom. Q'BASIC does allow complex statements on the command prompt but I don't like it.

I am thinking of only allowing a subset of the language to be interpreted interactively. For example no loops, no case select statements, no functions, etc. Code containing complex statements can be saved on a text file separately and loaded on the console.

Also, modern languages like to use a semicolon to denote the end of a code statement. I prefer the semicolon over the carriage return as a delimiter because of long statements. Sometimes to make the code prettier I want to break down a long statement into multiple lines. I can do this the semicolon but not with the carriage return.

The first version of AFOS BASIC will be what I call an interpreter masking over JAVA. What I mean by that is that BASIC will be at the surface (what you see) and JAVA will be underneath (doing all the work). The term masking meaning BASIC is just a mask that JAVA is wearing. (note: masking should be a vocabulary word).

To start simple I will only adopt four primitive data types.

byte - represented by the byte in JAVA (8bit signed)

integer - represented by the int in JAVA (32bit signed)

float - represented by float in JAVA

string - represented by the string in JAVA

Variable declaration is as follows:

[static] Var [shared] symbolname = expression[, symbolname = expression]

I tried to avoid AndroidStudio. It is possible to develop apps with just the command line tools. Unfortunately F-Droid is deprecating the old way in favor of gradle. To me it ultimately meant I have to have AndroidStudio installed even if I choose not to use it. I am forced to use it to create new projects because of the gradle scripts and initial file structure.

To jump start AFOS BASIC I resurrected an old project and imported it to use gradle. Eval is a simple interpreter, I developed a while back. I am going to overhaul it to make it into a BASIC interpreter. Eval is a very simple program.

Eval works like a command console or chat box. It uses only two GUI widgets. A TextEdit for input and a ListView for output. Every time you hit enter, the program takes the input, parses it, creates an syntax tree, evaluates the syntax tree and adds the output to the ListView.