@prefix : <http://yosi.us/unlambda#> .
#@prefix log: <http://www.w3.org/2000/10/swap/log#> .
@keywords a, of, is .
#
# An combinators interpreter.n3
# usage: cwm un_expr.n3 --think=unlambda.n3 --filter=un_filter.n3
# see un_expr.n3 for examples

#
# Begin defining what needs to be eval'ed
{?x a RootExpression} => {?x a NeedsEval} .

#recursive step of eval #1
{(?x ?y) a NeedsEval}
=>
{?x a NeedsEval .
 ?y a NeedsEval} .

#{?x a NeedsEval; log:rawType log:Other} => {?x eval ?x} .
#base case of eval
{k a NeedsEval} => {k eval k} .
{s a NeedsEval} => {s eval s} .
{v a NeedsEval} => {v eval v} .
{i a NeedsEval} => {i eval i} .

#
# Eval calls apply
{ (?x ?y) a NeedsEval .
 ?x eval ?a .
 ?y eval ?b .
} 
=>
{(?a ?b) a NeedsApply} .

#
#Eval gets the return value from apply, and returns it
{(?x ?y) a NeedsEval .
 ?x eval ?a .
 ?y eval ?b .
 (?a ?b) apply ?c . }
=>
{(?x ?y) eval ?c } .

#
#apply (k x)
{(k ?x) apply (k ?x)}
<= 
{(k ?x) a NeedsApply} .


#apply ((k y) x) ==> y
#
{((k ?y) ?x) apply ?y}
<=
{((k ?y) ?x) a NeedsApply} .

# apply (s x)
#
{(s ?x) apply (s ?x)}
<= 
{(s ?x) a NeedsApply} .

# apply ((s y) x)
#
{((s ?y) ?x) apply ((s ?y) ?x)}
<=
{((s ?y) ?x) a NeedsApply } .

# apply (((s z) y) x)
# calls (z x) and (y x)
{(((s ?y) ?z) ?x) a NeedsApply .
} =>
{(?y ?x) a NeedsEval .
 (?z ?x) a NeedsEval } .

# apply (((s z) y) x)
# gets (z x) and (y x)
# and calls ((z x) (y x))
{(((s ?y) ?z) ?x) a NeedsApply .
 (?y ?x) eval ?r .
 (?z ?x) eval ?s .
}
=>
{(?r ?s) a NeedsEval} .
# apply (((s z) y) x)
# gets ((z x) (y x))
# and returns it
{(((s ?y) ?z) ?x) a NeedsApply .
 (?y ?x) eval ?r .
 (?z ?x) eval ?s .
 (?r ?s) eval ?w }
=>
{(((s ?y) ?z) ?x) apply ?w} .

# (i x) ==> x
#
{(i ?x) apply ?x}
<= 
{(i ?x) a NeedsApply} .

# (v x) ==> v
#
{(v ?x) apply v}
<=
{(v ?x) a NeedsApply} .