🔮 🔪 💣 (CBKB) is the reference implementation of the Functional Emoji Programming Language (FEPL).
FEPL is a complete functional programming language. Specifically, it is an untyped ML-like language. It has a small feature set but is still very expressive. CBKB adds some extra features on top of the core FEPL language.
The core FEPL features are the following.
- Pattern matching
- Functions defined by equations
- Ad hoc algebraic datatypes
- Simple module system
CBKB adds the following additional feature.
- Two-way FFI with JavaScript
The syntax of the language is very simple. We will give a short overview here, but we invite you to read through the official grammar used to build the parser. It's only about 200 lines.
In this overview, we will use a grammar pseudocode. Names in bold refer to reserved words in FEPL, and names in italics refer to programmer inputs.
A module is a sequence of statements followed by a sequence of declarations.
A statement is either an import statement (FEPL modules) or an include statement (CBKB JavaScript FFI).
- import name imports the module name into the current module. All declarations made within name are now available in the current module.
- include path requires the given javascript file within the current
module. Specifically, a line of the form
var p = require(path)is emitted, wherepis the final component of path, i.e. the file name. This type of statement is added by CBKB to allow for FFI with JavaScript.
A declaration is either an FFI declaration or a function declaration.
- ffi ident string makes the JavaScript function identified by string available as an FEPL function identified by ident. In CBKB this emits a wrapper function that marshals FEPL data to JavaScript and back. The marshalling rules are at this time not clear.
- fn ident (alt pattern (sep pattern)* bind expr)+ defines a function called ident with at least one equation.
An expr is either a literal or a function application. A function application is just a sequence of expressions.
FEPL has the following literals.
- digit+ end_number is an integer literal.
- quote non-quote+ quote is a string literal.
- true|false is a boolean literal.
- lbracket rbracket | lbracket expr (asep expr)* rbracket is a tuple.
- package string expr? is an ad-hoc sum type with constructor string and optionally with wrapped value expr.
- lambda pattern (sep pattern)* bind expr is a function literal or lambda function. Notice that lambda functions cannot perform case analysis in their definition.
Patterns are the basis for pattern matching, which is how choice is encoded in FEPL. Patterns are very similar to literals.
- wild matches anything but does not create a binding to the matched expression's value.
- ident matches anything and creates a binding of ident to the matched value.
- integer matches an equal integer.
- string matches an equal string.
- bool matches an equal boolean.
- lbracket rbracket | lbracket pattern (asep pattern)* rbracket matches a tuple of same length, and sub-patterns must match elements of the value.
- package pattern pattern? matches an ad hoc sum type. If the second pattern is omitted, then only empty sum types are matched. If the second pattern is given as a wildcard, then both empty and non-empty sum types are matched.
Functions can only be matched by identifiers and wildcards.