→ CONTEXT: Final project for Fundamentals of Programming Languages (FLP), Universidad del Valle, 2022–2023
Reading about how programming languages work is abstract. The course asked us to build one: a language with its own grammar, an interpreter that executes it, and a REPL to try it live.
A language and interpreter written in Racket with the EOPL toolkit (#lang eopl). sllgen generates the scanner and parser from the grammar; the evaluator walks the AST with environments that support variables, let and letrec, assignment, procedures, methods and objects with send, update and clone. A REPL evaluates each expression live, and the AST of any program can be inspected to see how it was understood.
* primitives take their operands in parentheses *
--> +(2, *(3, 4))
14
--> let x = 5, y = 10 in *(x, y) end
50
* letrec: recursive procedures, with if / is *
--> letrec fact(n) = if is(n, 0) then 1 else *(n, apply fact(-(n, 1))) end in apply fact(5) end
120
* methods receive self first; objects hold fields and methods *
--> let m = meth(s, n) +(n, 1) end in apply m(7, 6) end
7
--> let casita = object{ z => 1 m => meth(s, n) +(n, 1) end } in send casita.m(41) end
42
A from-scratch language and interpreter that turned parsing, environments and evaluation into working code, with a REPL to run every expression live.
sllgen generates the scanner and parser from the grammar specification, so the effort went into semantics: environments, evaluation rules and objects.
Instead of: A recursive-descent parser written by hand
set needs mutable bindings. Storing values in vectors behind the environment keeps let, letrec and set consistent with each other.
Instead of: Immutable environments with no assignment
It let us explore object semantics (state, dispatch, cloning) on top of the functional core without building a class system.
Instead of: Procedures and records only
Grammar to interpreter in one pipeline: sllgen scanner and parser, AST datatypes and an environment-based evaluator
Objects, methods and clone semantics on top of a functional core with let, letrec, procedures and apply
A REPL to run programs live, with the AST available for inspection: parsing and evaluation made visible instead of theoretical
