codin9cafe[2015.03.04]Open course(programming languages) - 장철호(Ch Jang)

1. Programming Languages
Building a Web Brower
Instructor : Westley Weimer
1

2. 2

3. 3
Interpreting
Finds the meaning of a program by traversing its parse tree
+
+ 3
1 2
Parse Tree
is means ＂6＂

4. 4
Interpreting
required to check the types
One goal of semantic analysis is to notice and rule out bad programs
1 +＂hello＂
+
1 ＂hello＂
is means ?

5. 5
HTML Interpreting
＂<b>hello</b>＂
Syntactical
Analysis
Lexical
Analysis
[('tag-element', 'b', [], [('word-element', 'hello')], 'b')]

6. 6
HTML Interpreting
[('tag-element', 'b', [], [('word-element', 'hello')], 'b')]
tag-element
b word-element
hello
b
＂<b>hello</b>＂

7. 7
HTML Interpreting
[('tag-element', 'b', [], [('word-element', 'hello')], 'b')]
tag-element
b word-element
hello
b
＂<b>hello</b>＂

8. 8
HTML Interpreting
[('tag-element', 'b', [], [('word-element', 'hello')], 'b')]
tag-element
b word-element
hello
b
＂<b>hello</b>＂

9. 9
HTML Interpreting
[('tag-element', 'b', [], [('word-element', 'hello')], 'b')]
tag-element
b word-element
hello
b
＂<b>hello</b>＂

10. 10
HTML Interpreting
import graphics
def interpret(trees):
for tree in trees:
# ("word-element", "hello")
nodetype=tree[0]
if nodetype == "word-element":
graphics.word(tree[1])
# [("tag-element", "b", [], [("word-element", "hello")], "b")]
elif nodetype == "tag-element“:
tagname = tree[1]
tagargs = tree[2]
subtrees = tree[3]
closetagname = tree[4]
"<a href=‘www.codin.com’>codin9cafe</a>"
graphics.begintag(‘a’, {‘href’ : ’www.codin.com’})
graphics.word(‘codin9cafe’)
graphics.endtag()
codin9cafe

11. 11
HTML Interpreting
if tagname != closetagname:
graphics.warning("mismatched tag")
else:
graphics.begintag(tagname,tagargs)
interpret(subtrees)
graphics.endtag()
graphics.initialize() # Enables display of output.
interpret([("word-element","Hello")])
interpret([("tag-element","a",[],[("word-element","Hello")],"b")])
graphics.finalize() # Disables display of output.

12. 12
JS Interpreting
＂ x = 3 + 6＂
Syntactical
Analysis
Lexical
Analysis
(‘assign’, ’x’, (‘binop’, (‘number’, 3.0), ‘+’, (‘number’, 6.0)))

13. 13
JS Interpreting
(‘assign’, ’x’, (‘binop’, (‘number’, 3.0), ‘+’, (‘number’, 6.0)))
assign
x
+
＂x = 3 + 6＂
number number
3.0 6.0
binop

14. 14
JS Interpreting
(‘assign’, ’x’, (‘binop’, (‘number’, 3.0), ‘+’, (‘number’, 6.0)))
assign
x
+
＂x = 3 + 6＂
number number
3.0 6.0
binop

15. 15
JS Interpreting
(‘assign’, ’x’, (‘binop’, (‘number’, 3.0), ‘+’, (‘number’, 6.0)))
assign
x
+
＂x = 3 + 6＂
number number
3.0 6.0
binop

16. 16
JS Interpreting
(‘assign’, ’x’, (‘binop’, (‘number’, 3.0), ‘+’, (‘binop’, (‘number’, 6.0)))
assign
x
+
＂x = 3 + 6＂
number number
3.0 6.0
binop

17. 17
JS Interpreting
def eval_stmts(tree, environment):
stmttype = tree[0]
if stmttype == "assign":
# ("assign", "x", ("binop", ..., "+", ...))
variable_name = tree[1]
right_child = tree[2]
new_value = eval_exp(right_child, environment)
env_update(environment, variable_name, new_value)
to know the current state
ex) env = { “x” : 3 }
x + 2 = 5

18. 18
JS Interpreting
def eval_exp(tree, environment):
nodetype = tree[0]
if nodetype == "number":
return int(tree[1])
elif nodetype == "binop":
left_value = eval_exp(tree[1], environment)
operator = tree[2]
right_value = eval_exp(tree[3], environment)
if operator == "+":
return left_value + right_value
elif nodetype == "identifier":
# ("binop", ("identifier","x"), "+", ("number","2"))
identifier = tree[1]
return env_lookup(environment,identifier)

19. 19
JS Interpreting
x = 1
y = 2
def myfun(x):
print x
print y
myfun(5)
x : 1 y : 2
Global Environment
x : 5
New Environment
env = (None, {"x":1, “y":1})
newenv = (env, {"x":5})

20. 20