A Pure Lisp implementation for Fundamental Concepts Implementation Game.
- PureScript v0.13.2
- Spago v0.8.5.0
- Node v12.6.0
spago test
Everything is an expression in FCILisp.
Expressions consist of lists and others, called atoms.
Atoms are further subdevided.
FCILisp has pairs and atoms as first-class objects (hereafter, the first-class object is called "value").
Atoms are natural numbers, symbols, functions, and recursive functions.
Note that the term "atom" is used here in two senses, one as a grammer and the other as data.
Atoms are just strings that are not lists.
t and nil are special symbols.
Only nil is falsy, and any other value is truthy.
You can use t to represent explicitly truthy.
They are true and false in other languages.
Internally it wraps a PureScript Int type, so is a 32-bit unsigned interger.
See the Puresuit.
Symbols are non-litaral strings of available charactgers.
You can use alphanumeric characters and symbols: !, @, #, $, %, ^, &, *, -, _, =, +, \, ~, |, ;, :, ', ", ,, <, ., >, /, ?.
So far symbols are strins that are not nutural number literals, but in the future it may be strings that not another literals, such as quoted symbol literals, character literals, or string literals.
Symbols can be bound to values and can be treated as variables.
In FCILisp, all variables are constant and all values are immutable.
As in other functional languages, functions are first-class objects in FCILisp, so they can be passed to functions, bound to symbols, and create instances in FCILisp.
(fun x (+ x 2))fun takes only one name and one expression each.
To create a function with multiple arguments, you can nest it.
(fun x (fun y (+ x y)))fun can not express recursion. That's because functions created with fun have no way to call themselves.
recur can take a name that binds itself, so generated functions can invoke itself recursively.
(recur fact n (if (= n 0) 1 (* n (fact (- n 1)))))There are no such value as lists, just pairs in FCILisp.
But you can construct lists by using pairs as below.
(cons 0 (cons 1 (cons 2 nil))) ;; this can be considered a list like '(0 1 2)cons stands for "constructor" and takes two expressions and returns a pair value.
Of course it can also behave as a pair.
Builtin predicates can have multiple arguments.
Takes one expression and returns nil if it is a pair, otherwise returns t.
Because it is an atom other than a pair.
nil, t, and natural numbers are comparable.
Other functions, recursive functions, and pairs are not comparable.
Symbols are evaluated to one of the above.
In the future, if quote is implemented, the symbol will also be comparable.
Operators are builtin functions and can have multiple arguments.
Takes one pair and returns the left value from it.
When you look at a pair as a list, this operation can be seen as getting the top element.
Takes one pair and returns the right value from it.
When you look at a pair as a list, this operation can be seen as getting the rest except the first element.
Takes two natural numbers and returns the sum of them.
Takes two natural numbers and returns their difference, but returns 0 if it is less than 0
Takes two natural numbers and returns their product.
Takes two natural numbers and returns the natural number that is their quotient.
An error occurs if the second argument is 0.
Takes two natural numbers and returns their remainder.
An error occurs if the second arguments is 0.
Takes two natural numbers and returns t if the first is less than the second, otherwise returns nil.
Takes two natural numbers and returns t if the first is greater than the second, otherwise returns nil.
Conditions does not necessarily evaluate arguments in advance.
Takes a conditional expression and two expressions, evaluate the third expression if the evaluation result of the conditional expression is nil, otherwise evaluate the second expression.
Always one of the expressions is not evaluated.
Take one of a predicate, an operator, a function, and a recursive function and expressions, and returns the result of applying the expressions to them.
Symbols are evaluated to one of the above.
In addition, functions and recursive functions always take only one argument.