计算机代写 CSE 11 – cscodehelp代写

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27 February 2019 OSU CSE 1

BL Compiler Structure
string of characters (source code)

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string of tokens (“words”)
abstract program
integers (object code)
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A BL program consists of some statements …
Code Generator

• The Statement component family allows you to manipulate values that are ASTs for
BL statements
• The mathematical model of a Statement value is a tree of STATEMENT_LABEL with some constraints
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IF condition
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CALL instruction
WHILE condition
IF_ELSE condition

IF condition
A Statement variable’s value is a
STATEMENT_LABEL
IF_ELSE condition
with some constraints, so we use rather than
to illustrate its recursive structure.
WHILE condition
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The kind of statement
(based on the root)
determines how many
and which kinds of
children it may have.
IF condition
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CALL instruction
WHILE condition
IF_ELSE condition

The children of a BLOCK statement may not be BLOCK statements.
IF condition
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CALL instruction
WHILE condition
IF_ELSE condition

The child of an IF or WHILE statement must be a BLOCK statement.
IF condition
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CALL instruction
WHILE condition
IF_ELSE condition

The two children of an IF_ELSE statement must be BLOCK statements.
IF condition
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CALL instruction
WHILE condition
IF_ELSE condition

A CALL statement has no children.
IF condition
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CALL instruction
WHILE condition
IF_ELSE condition

Interfaces and Classes
Statement- Kernel
implements
Statement1
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OSU CSE 11

Interfaces and Classes
Statement- Kernel
implements
Statement1
StatementKernel
has contracts for 12 methods that involve “assembling” and “disassembling” the various BL statements (similar to Tree methods).
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OSU CSE 12

Interfaces and Classes
has these additional methods (not
discussed here):
parseBlock
prettyPrint
Statement- Kernel
implements
Statement1
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OSU CSE 13

Enumerations
• Java has a special construct, enum (short
for “enumeration”), that easily allows you
to use meaningful symbolic names where
you might otherwise be inclined to declare int variables and give them arbitrary
values to participate just in equality tests
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Example: The Kind Enum
• TheinterfaceStatementKernel contains this code:
* The kinds of statements.
enum Kind {
BLOCK, IF, IF_ELSE, WHILE, CALL
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Kind Enum m:
final int BLOCK = 1; final int IF = 2;
You may not do arithmetic with the contains this code:
enum constants, where you could /**
• TheinterfaceStatementKernel …
with the int constants above.
* The kinds of statements.
enum Kind {
BLOCK, IF, IF_ELSE, WHILE, CALL
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Example: The Condition Enum
* The possible conditions for IF, IF_ELSE, * and WHILE statements.
enum Condition {
NEXT_IS_EMPTY, NEXT_IS_NOT_EMPTY, NEXT_IS_WALL, NEXT_IS_NOT_WALL, NEXT_IS_FRIEND, NEXT_IS_NOT_FRIEND, NEXT_IS_ENEMY, NEXT_IS_NOT_ENEMY, RANDOM, TRUE
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Mathematical Model (1)
IDENTIFIER is string of character exemplar id
constraint
[id starts with a letter ‘a’-‘z’, ‘A’-‘Z’] and
[id contains only letters, digits ‘0’-‘9’, and ‘-‘] and
[id is not one of the keywords or
conditions in the BL language]
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Mathematical Model (2)
STATEMENT_LABEL is ( kind: Kind,
test: Condition,
call: IDENTIFIER) exemplar sl constraint
[if sl.kind = BLOCK then sl.test and sl.call are irrelevant] and
[if sl.kind = IF or sl.kind = IF_ELSE or
sl.kind = WHILE then sl.call is irrelevant] and
[if sl.kind = CALL then sl.test is irrelevant]
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Mathematical Model (2) Notice the use of the enums
STATEMENT_LABEL is ( kind: Kind,
test: Condition,
call: IDENTIFIER) exemplar sl constraint
in this model, as well as the previously defined IDENTIFIER.
[if sl.kind = BLOCK then sl.test and sl.call are irrelevant] and
[if sl.kind = IF or sl.kind = IF_ELSE or
sl.kind = WHILE then sl.call is irrelevant] and
[if sl.kind = CALL then sl.test is irrelevant]
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Mathematical Model (3)
STATEMENT_MODEL is tree of STATEMENT_LABEL exemplar s
constraint
|s| > 0 and
[BLOCK can have 0 or more children, but
not another BLOCK as a child] and
[IF must have exactly one BLOCK child] and [IF_ELSE must have exactly two BLOCK
children] and
[WHILE must have exactly one BLOCK child] and [CALL must have no children (must be a leaf)]
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Mathematical Model (4)
type StatementKernel is modeled by STATEMENT_MODEL
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No-argument Constructor • Ensures:
this = compose((BLOCK, ?, ?), <>)
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No-argument Constructor • Ensures:
this = compose((BLOCK, ?, ?), <>) The use of ? here means we do not know—and,
frankly, do not care about—the values of the 2nd and 3rd tuple components (test and call); the
model says they are irrelevant if the 1st tuple component (kind) is BLOCK.
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Statement s =
new Statement1();
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Statement s =
new Statement1();
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Statement.Kind kind()
• Reports the kind of statement this is. • Ensures:
kind = [the statement kind of this]
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Kind k = s.kind();
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Kind k = s.kind();
s = BLOCK k = BLOCK
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addToBlock
void addToBlock(int pos, Statement s)
• Adds the statement s at position pos in this BLOCK statement.
• Updates: this
• Clears: s
• Requires:
[this is a BLOCK statement] and [s is not a BLOCK statement] and 0 <= pos <= [length of this BLOCK] • Ensures: this = [#this with child #s inserted at position pos] 27 February 2019 s = BLOCK ns = s.addToBlock(1, 27 February 2019 OSU CSE 31 s = BLOCK ns = s.addToBlock(1, 27 February 2019 OSU CSE 32 removeFromBlock Statement removeFromBlock(int pos) • Removes and returns the statement at position pos of this BLOCK statement. • Updates:this • Requires: [this is a BLOCK statement] and 0 <= pos < [length of this BLOCK] • Ensures: this = [#this with child at position pos removed and returned as result] 27 February 2019 OSU CSE Statement ns = s.removeFromBlock(1); 27 February 2019 OSU CSE 34 Statement ns = s.removeFromBlock(1); 27 February 2019 OSU CSE 35 lengthOfBlock int lengthOfBlock() • Reports the number of statements in this BLOCK statement. • Requires: [this is a BLOCK statement] • Ensures: lengthOfBlock = [the number of children of this] 27 February 2019 OSU CSE assembleIf void assembleIf(Statement.Condition c, Statement s) • Assembles in this a statement with root label (IF, c , ?) and only subtree the BLOCK s; the declaration notwithstanding, the dynamic type of s must be the same as the dynamic type of this. • Replaces: this • Clears: s • Requires: [s is a BLOCK statement] • Ensures: this = compose((IF, c, ?), <#s>) 27 February 2019 OSU CSE

s = ? ns =
s.assembleIf(
RANDOM, ns);
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s = ? ns =
s.assembleIf(
RANDOM, ns);
s= RANDOM ns=
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disassembleIf
Statement.Condition disassembleIf(
Statement s)
• Disassembles IF statement this into its test Condition, which is
returned as the value of the function, and its only subtree, the BLOCK statement s; the declaration notwithstanding, the dynamic type of s must be the same as the dynamic type of this.
• Replaces: s
• Clears: this
• Requires:
[this is an IF statement]
• Ensures:
#this = compose((IF, disassembleIf, ?), ) 27 February 2019 OSU CSE

s = TRUE ns = ?
Condition c =
s.disassembleIf(ns);
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s = TRUE ns = ?
Condition c =
s.disassembleIf(ns);
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Other Methods
• See the Javadoc for Statement for details of the other methods:
– assembleIfElse
– disassembleIfElse – assembleWhile
– disassembleWhile – assembleCall
– disassembleCall
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IF condition
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CALL instruction
WHILE condition
IF_ELSE condition

“Processing” a Statement
if (s.kind() == BLOCK) { … }
else if (s.kind() == IF) { … } else if (s.kind() == IF_ELSE) { … } else if (s.kind() == WHILE) { … } else if (s.kind() == CALL) { … }
27 February 2019 OSU CSE 45

“Processing” a Statement
if (s.kind() == BLOCK) { … }
else if (s.kind() == IF) { … } else if (s.kind() == IF_ELSE) { … } else if (s.kind() == WHILE) { … } else if (s.kind() == CALL) { … }
Technically, there is no reason you need to test this last condition; because what else could it be?
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Java’s switch Construct
switch (s.kind()) {
case BLOCK: { … ; break;} case IF: { … ; break;} case IF_ELSE: { … ; break;} case WHILE: { … ; break;} case CALL: { … ; break;} default: { … ; break;}
27 February 2019 OSU CSE 47

Java’s switch Construct
switch (s.kind()) {
case BLOCK: { … ; break;} case IF: { … ; break;} case IF_ELSE: { … ; break;} case WHILE: { … ; break;} case CALL: { … ; break;} default: { … ;}
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if-else-if-else-if-… OSU CSE 48
The switch is recommended over a long string of

Java’s switch Construct
switch (s.kind()) {
case BLOCK: { … ; break;} case IF: { … ; break;} case IF_ELSE: { … ; break;} case WHILE: { … ; break;} case CALL: { … ; break;} default: { … ;}
The default case is recommended even when
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technically it is not needed (as here).

• OSU CSE Components API: Statement
– http://cse.osu.edu/software/common/doc/ • Big Java, Section 5.3
– http://osu.worldcat.org/title/big-java/oclc/754642794
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