Statement 27 February 2019 OSU CSE 1 BL Compiler Structure Code - - PowerPoint PPT Presentation

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Statement 27 February 2019 OSU CSE 1 BL Compiler Structure Code - - PowerPoint PPT Presentation

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Statement 27 February 2019 OSU CSE 1 BL Compiler Structure Code Tokenizer Parser Generator string of string of abstract string of characters tokens program integers (source code) (words) (object code) A BL program consists

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Statement

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BL Compiler Structure

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Code Generator Parser Tokenizer string of characters (source code) string of tokens (“words”) abstract program string of integers (object code)

A BL program consists of some statements …

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Statement

  • 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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BLOCK IF condition WHILE condition CALL instruction

s =

IF_ELSE condition

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BLOCK IF condition WHILE condition CALL instruction

s =

IF_ELSE condition

A Statement variable’s value is a tree of STATEMENT_LABEL with some constraints, so we use rather than to illustrate its recursive structure.

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BLOCK IF condition WHILE condition CALL instruction

s =

IF_ELSE condition

The kind of statement (based on the root) determines how many and which kinds of children it may have.

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BLOCK IF condition WHILE condition CALL instruction

s =

IF_ELSE condition

The children of a BLOCK statement may not be BLOCK statements.

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BLOCK IF condition WHILE condition CALL instruction

s =

IF_ELSE condition

The child of an IF or WHILE statement must be a BLOCK statement.

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BLOCK IF condition WHILE condition CALL instruction

s =

IF_ELSE condition

The two children of an IF_ELSE statement must be BLOCK statements.

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BLOCK IF condition WHILE condition CALL instruction

s =

IF_ELSE condition

A CALL statement has no children.

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Interfaces and Classes

Statement- Kernel extends Standard extends

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Statement implements Statement1

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Interfaces and Classes

Statement- Kernel extends Standard extends

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Statement 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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Interfaces and Classes

Statement- Kernel extends Standard extends

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Statement implements Statement1 Statement has these additional methods (not discussed here): parse parseBlock prettyPrint

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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

  • The interface StatementKernel

contains this code:

/** * The kinds of statements. */ enum Kind { BLOCK, IF, IF_ELSE, WHILE, CALL }

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Example: The Kind Enum

  • The interface StatementKernel

contains this code:

/** * The kinds of statements. */ enum Kind { BLOCK, IF, IF_ELSE, WHILE, CALL }

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This is quite different from: final int BLOCK = 1; final int IF = 2; ... You may not do arithmetic with the enum constants, where you could with the int constants above.

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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)

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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Notice the use of the enums in this model, as well as the previously defined IDENTIFIER.

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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, ?, ?), <>)

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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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Example

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Code State

Statement s = new Statement1();

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Example

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Code State

Statement s = new Statement1();

s =

BLOCK

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kind

Statement.Kind kind()

  • Reports the kind of statement this is.
  • Ensures:

kind = [the statement kind of this]

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Example

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Code State

s =

Kind k = s.kind();

BLOCK

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Example

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Code State

s =

Kind k = s.kind();

s = k = BLOCK

BLOCK 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]

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Example

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Code State

s = ns =

s.addToBlock(1, ns);

BLOCK

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Example

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Code State

s = ns =

s.addToBlock(1, ns);

s = ns =

BLOCK BLOCK BLOCK

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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]

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Example

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Code State

s = Statement ns = s.removeFromBlock(1);

BLOCK

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Example

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Code State

s = Statement ns = s.removeFromBlock(1); s = ns =

BLOCK BLOCK

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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]

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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>)

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Example

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Code State

s = ? ns =

s.assembleIf( RANDOM, ns);

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Example

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Code State

s = ? ns =

s.assembleIf( RANDOM, ns);

s = ns =

IF RANDOM

BLOCK

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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, ?), <s>)

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Example

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Code State

s = ns = ? Condition c = s.disassembleIf(ns);

IF TRUE

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Example

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Code State

s = ns = ? Condition c = s.disassembleIf(ns); ns = s = c = TRUE

IF TRUE

BLOCK

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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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BLOCK IF condition WHILE condition CALL instruction

s =

IF_ELSE condition

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“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) { ... }

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“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) { ... }

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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;} }

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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: { ... ;} }

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The switch is recommended

  • ver a long string of

if-else-if-else-if-...

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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: { ... ;} }

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The default case is recommended even when technically it is not needed (as here).

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Resources

  • 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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