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3 changes: 3 additions & 0 deletions lib/lisp.rb
Original file line number Diff line number Diff line change
Expand Up @@ -53,6 +53,9 @@ def self.execute expression, scope = global
_, test, consequent, alternative = expression
expression = if execute test, scope then consequent else alternative end
execute expression, scope
when :quote
_, expression = expression
expression
when :set!
_, var, expression = expression
if scope.has_key?(var) then scope[var] = execute expression, scope else raise "#{var} is undefined" end
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5 changes: 5 additions & 0 deletions test/test_lisp.rb
Original file line number Diff line number Diff line change
Expand Up @@ -52,6 +52,11 @@ def test_set!
assert_raises(RuntimeError) { Lisp.eval("(set! foo 0)") }
end

def test_quote
assert_equal [1,2,3], Lisp.eval("(quote (1 2 3))")
assert_equal [0,1,2,3], Lisp.eval("(+ (quote (0)) (quote (1 2 3)))")
end

def test_begin
assert_equal 4, Lisp.eval("(begin (define x 1) (set! x (+ x 1)) (* x 2))")
end
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