class Lisp | |
Fs = { | |
:label => lambda {|name,value| Fs[name] = lambda { value } }, | |
:car => lambda {|sexp| sexp.first }, | |
:cdr => lambda {|sexp| sexp.slice(1, sexp.size) }, | |
:cons => lambda {|head,tail| [head] + tail }, | |
:atom => lambda {|sexp| !sexp.is_a?(Array) }, | |
:eq => lambda {|a,b| a == b }, | |
:if => lambda {|cnd,thn,els| cnd ? thn : els } | |
} | |
def self.parse fn, *sexp | |
return sexp.flatten(1) if fn == :quote | |
args = sexp.map { |a| Fs[:atom].call(a) ? a : parse(*a) } | |
Fs.key?(fn) ? Fs[fn].call(*args) : fn | |
end | |
end | |
describe Lisp do | |
it "works with nested sexps" do | |
Lisp.parse(:eq, [:quote, [1, 2, 3]], [:cons, 1, [:quote, [2,3]]]).should == true | |
Lisp.parse(*Lisp.parse(:quote, [:cons, 1, [:quote, [2,3]]])).should == [1, 2, 3] | |
end | |
describe ":quote" do | |
it "returns the sexp" do | |
Lisp.parse(:quote, [:eq, 1, 2]).should == [:eq, 1, 2] | |
end | |
it "returns the value" do | |
Lisp.parse(:quote, [1, 2]).should == [1, 2] | |
end | |
end | |
describe ":car" do | |
it "returns the head of the sexp" do | |
Lisp.parse(:car, [:quote, [1, 2]]).should == 1 | |
end | |
end | |
describe ":cdr" do | |
it "returns the tail of the sexp" do | |
Lisp.parse(:cdr, [:quote, [1, 2, 3]]).should == [2, 3] | |
end | |
end | |
describe ":cons" do | |
it "concats the the first argument to the second" do | |
Lisp.parse(:cons, 1, [:quote, [2, 3]]).should == [1, 2, 3] | |
end | |
end | |
describe ":if" do | |
it "returns the third sexp if the first is true" do | |
Lisp.parse(:if, [:eq, 2, 2], 42, 43).should == 42 | |
end | |
it "returns the second sexp if the first is false" do | |
Lisp.parse(:if, [:eq, 1, 2], 42, 43).should == 43 | |
end | |
end | |
describe ":atom" do | |
it "returns true if it's an atom" do | |
Lisp.parse(:atom, 42).should == true | |
end | |
it "returns false if it's not an atom" do | |
Lisp.parse(:atom, [:quote, [42]]).should == false | |
end | |
it "returns false if it's not an atom" do | |
Lisp.parse(:atom, [:quote, [42, 43]]).should == false | |
end | |
end | |
describe ":eq" do | |
it "returns true if values are equal" do | |
Lisp.parse(:eq, 42, 42).should == true | |
end | |
it "returns false if values are equal" do | |
Lisp.parse(:eq, 42, 43).should == false | |
end | |
end | |
describe ":label" do | |
it "sets the value" do | |
Lisp.parse(:label, :a, 42) | |
Lisp.parse(:a).should == 42 | |
end | |
end | |
end |
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