apiel

Apiel is a small subset of the APL programming language implemented in Rust.

The ultimate goal of the project is to export a macro that allows evaluating APL expressions from Rust code, providing a way to solve some problems in a very conscise manner.

Affiliation

This is my capstone project for the rustcamp, a Rust bootcamp organized by the Ukrainian Rust Community (website, linked in, telegram, github, youtube, twitter).

Array languages

APL was the first language in an "Array programming" or "Iversonian" paradigm. These languages are closer to mathematical notation than to C-like programming languages. The concepts proposed by APL inspired many similar languages, influenced the development of the functional programming paradigm, and had a giant impact on programming as a whole.

Approach

The project utilizes Yacc (Yet-Another-Compiler-Compiler) implementation in Rust through grmtools to build the lexer and parser.

apiel.l contains the tokens for the lexer, apiel.y describes the Yacc grammar. The build.rs generaters Rust code for the lexer and parser generator.

My main entry point is apiel/src/parse/mod.rs. There is fn parse_and_evaluate() that runs parse::eval() (located in /parse/eval.rs) on the expression passed to it. The parse::eval() contains a single match expression that performs operations on the data contained in the Expr enumeration according to the expression type (it always calls parse::eval() recursively for lhs and rhs of the expression). The Expr enumeration is defined in aliel.y. Ech variant of the Expr usually contains a Span identifying where it's located in the original input, and boxed arguments, which allows for unlimited recursion inside the expression.

Usage

cargo run or RUST_LOG=debug cargo run for debugging output.

Enter commands in the terminal.

List of supported glyphs and operations:

Glyph	Monadic operation	Impl.	Dyadic operation	Impl.
+	Conjugate	✅*	Addition	✅
-	Negate	✅	Subtraction	✅
×	Direction	✅	Multiplication	✅
÷	Reciprocal	✅	Division	✅
*	Exponentiation	✅	Raising to power	✅
⍟	Natural logarithm	✅	Logarithm	✅
⌹	Matrix inverse	-	Matrix divide	-
○	Pi Multiple	✅	Circular functions	-
!	Factorial	✅	Binomial	✅
?	Roll	✅	Deal	✅
|	Magnitude	✅	Residue	✅
⌈	Ceil	✅	Maximum	✅
⌊	Floor	✅	Minimum	✅
⍳	Generate index	✅	Index of	-
⍸	Where	✅	Interval index	-
/	Replicate	-	Reduce	✅
\	Expand	-	Scan	-
,	Ravel	-	Catenate/Laminate	-
⍴	Shape	-	Reshape	-
.	-	-	Product	-
∘.	-	-	Outer Product	-
=	-	-	Equality	-
←	-	-	Assignment	-

• * - Not implemented for complex numbers

Usage examples

// Dyadic op. Division: vector by scalar
>>> 5 25 125 ÷ 5
Result: [1, 5, 25]
// Dyadic op. Addition: vector on vector
>>> 1 2 3 + 4 5 6
Result: [5, 7, 9]
// Monadic op. Addition: vector on vector
>>> + 1 2 3 
Result: [1, 2, 3]
>>> - 1 2 3 
Result: [-1, -2, -3]
>>> 1 2 3 × 2 4 6
Result: [2, 8, 18]
>>> 1 2 3 * 2 4 6         
Result: [1, 16, 729]
>>> * 1 2 3
Result: [2, 7, 20]
>>> ⍟ 1 2 3
Result: [0, 0, 1]
>>> ⍟ 5 10 100
Result: [1, 2, 4]
>>> 10 - 1 2 3
Result: [9, 8, 7]
>>> 20 40 60 ÷ 2 4     
Evaluation error at line 1 column 1: '', operands must be of the same size or one must be scalar.
>>> ⍟ 10 100 1000
Result: [2, 4, 6]
>>> ⌈ 3 6 9 1
Result: [9]
>>> ⌊ 5 10 29 1
Result: [1]