fava is a Turing complete, pure functional programming language, which was designed for the educational purpose in computational theory.

• Scalaで自作するプログラミング言語処理系 (PDF) (HTML)

$ gradle build
$ java -jar build/libs/fava.jar
which language do you use?
[0]: fava
[1]: math
[2]: univ
[3]: regl
[4]: lisp
select: 0
fava$

• fava supports some arithmetic, logic, and relational operations.

fava$ 114 + 514
628
fava$ 3 > 1? "LOOSE": "WIN"
LOOSE

• fava does not accept local variable and function declarations, and block statements are also prohibited.

fava$ ((x)=>(y)=>3*x+7*y)(2)(3)
27

• fava is Turing complete and can theoretically define boolean operations without using system functions.

fava$ ((l,r)=>l(r,(x,y)=>y))((x,y)=>x,(x,y)=>y)(true,false) // true & false
false
fava$ ((l,r)=>l((x,y)=>x,r))((x,y)=>x,(x,y)=>y)(true,false) // true | false
true

• fava is Turing complete and can theoretically define numeric operations without using system functions.

fava$ ((l,r)=>(f,x)=>l(f)(r(f)(x)))((f)=>(x)=>f(x),(f)=>(x)=>f(f(x)))((x)=>x+1,0) // 1 + 2
3
fava$ ((l,r)=>(f,x)=>l(r(f))(x))((f)=>(x)=>f(f(x)),(f)=>(x)=>f(f(x)))((x)=>x+1,0) // 2 * 2
4

• fava evaluates function arguments lazily.

fava$ ((f)=>((x)=>f(x(x)))((x)=>f(x(x))))((f)=>(n)=>(n==0)?1:n*f(n-1))(10)
3628800

• Functions and variables are declared in the same namespace.

elva$ (set ’function-in-variable list)
#<native form list>
elva$ (function-in-variable 1 2 3 4 5)
(1 2 3 4 5)

• Use the define-lambda macro to define a function.

elva$ (define-lambda fact (x) (if (eq x 1) x (* x (fact (- x 1)))))
(lambda (x) (if (eq x 1) x (* x (fact (- x 1)))))

• Use the define-syntax macro to define a macro or syntax.

elva$ define-lambda
(syntax (name pars body) (list (quote setq) name (list (quote lambda) pars body)))
elva$ define-syntax
(syntax (name pars body) (list (quote setq) name (list (quote syntax) pars body)))

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