1. A Quest for a Statically Typed Embeddable Programming Language
Project Fox
A Quest for a Statically Typed Embeddable Programming Language
Pierre van Houtryve

2. The Rabbit Hole Introduction:
(Illustration Source: )

3. Fox Learning Project Statically Typed
End goal: Embeddability in other Applications
Fox should be interoperable with C++
(Not an official logo, just an illustration . Source: )

4. How it’s Made: Compiler and Interpreters
(LLVM Logo)

5. The Lexer func foo(y: int) { let x: int = 3; }
Source
Kind
Location
“func”
FuncKw
1:1-1-4
“foo”
Identifier
1:6-1:8
“(“
LParen
1:9-1:9
“y”
1:10-1:10
“:”
Colon
1:11-1:11
“int”
IntKw
1:13-1:15
“)”
RParen
1:16-1:16
“{“
LBrace
1:18-1:18
“let”
LetKw
2:3-2:5 …
Converts the source code into tokens

6. IntegerLiteralExpr Value : 3
Source
Kind
Location
“func”
FuncKw
1:1-1-4
“foo”
Identifier
1:6-1:8
“(“
LParen
1:9-1:9
“y”
1:10-1:10
“:”
Colon
1:11-1:11
“int”
IntKw
1:13-1:15
“)”
RParen
1:16-1:16
“{“
LBrace
1:18-1:18
“let”
LetKw
2:3-2:5 …
The Parser
Consumes the tokens and produces the Abstract Syntax Tree (AST)
FuncDecl
Identifier: “foo”
CompoundStmt
Size: 1
VarDecl
Type: “int”
Identifier: “x”
IntegerLiteralExpr Value : 3
ParamDecl
Identifier: “y”

7. IntegerLiteralExpr Value : 3
FuncDecl
Identifier: “foo”
CompoundStmt
Size: 1
VarDecl
Type: “int”
Identifier: “x”
IntegerLiteralExpr Value : 3
ParamDecl
Identifier: “y”
Semantic Analysis
Checks the language’s semantics
Optional, mostly done in statically typed languages
Analyzes the AST, searching for errors, inconsistencies, etc.

8. IntegerLiteralExpr Value : 3
FuncDecl
Identifier: “foo”
CompoundStmt
Size: 1
VarDecl
Type: “int”
Identifier: “x”
IntegerLiteralExpr Value : 3
ParamDecl
Identifier: “y”
Code Generation
Generates something from the AST
Another existing programming language
E.g. TypeScript (JavaScript)
An Intermediate Representation
E.g. Clang (LLVM IR), Swift (SIL)
Bytecode for a Virtual Machine
E.g. Java (JVM BC), Fox (Fox VM BC)
Machine Code

9. How do you write one? Trial and Error of course!
FuncDecl
Identifier: “foo”
CompoundStmt
Size: 1
VarDecl
Type: “int”
Identifier: “x”
IntegerLiteralExpr Value : 3
ParamDecl
Identifier: “y”
The AST
Usually the first representation of the code built by the compiler/interpreter
A basic version is trivial to write, but it can get really complicated really fast as new language features are added.
How do you write one? Trial and Error of course!

10. Trial and Error Everywhere!
Not the fastest way of doing things, but you learn a lot!

11. Conclusion
Progress on Fox is slow, but I enjoy the journey because I learn a lot!
Fox:
A statically typed interpreted programming language
Learning Project
Relatively limited feature set, not really usable in its current state
GitHub: