The Book

Class: Blocks09

Seven~ Blocks09

Example 7/09: compile global functions with block structure.

new Blocks09()

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Extends

Classes

Block
Fun
Symbol
Var

Members

context

Manages a stack of contexts for assign or call to a name

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funct

Describes current function

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size

Manages next (global) variable address

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Methods

Do()

Do: 'do';

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Else()

Else: 'else';

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Then()

Then: 'then';

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While()

While: 'while'; returns address for branch to while

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_alloc()

Replace: returns new Var at next local/global address.

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_check_defs()

Flags undefined functions, returns main if defined

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_dcl()

Replace: sets innermost map, returns sym

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_find()

Replace: searches innermost to outermost blocks and global

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_startup(main)

[Extend] Push 0 for main parameters.

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Name Type Description
main Fun

describes main().
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add()

add: '+' product;

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args()

args: '(' [ sums ] ')'; expects context, codes call

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assign()

assign: symbol action; codes Pop, pops context

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begin()

begin: 'begin';

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block()

block: begin [ vars ] stmts 'end';

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divide()

divide: '/' signed;

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else()

else: Else [ vars ] stmts;

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eq()

eq: '=' sum;

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fun()

fun: head parms [ block ] ';';

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ge()

ge: '>=' sum;

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gt()

gt: '>' sum;

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head: 'function' Name; returns function symbol

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input()

input: 'input' [ Number ];

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le()

le: '<=' sum;

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loop()

loop: While cmp Do [ vars ] stmts 'od';

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lt()

lt: '<' sum;

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multiply()

multiply: '*' signed;

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name()

name: symbol [ args ]; codes variable load, pops context

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names()

names: Name [{ ',' Name }]; defines new variables, returns number of names

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ne()

ne: '<>' sum;

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number()

number: Number;

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parms()

parms: '(' [ names ] ')';

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print()

print: 'print' sums;

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prog()

prog: [ vars ] funs; returns executable

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return()

return: 'return' [ sum ];

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run()

Creates stack machine

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select()

select: 'if' cmp then [ else ] 'fi';

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signed()

signed: [ '-' ] term;

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stmt()

stmt: assign | print | loop | select; [replace] no op

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store()

store: '=' sum; expects context, codes assignment

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subtract()

subtract: '-' product;

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sum()

sum: 'let' Name '=' sum | product [{ add | subtract }];

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sums()

sums: sum [{ ',' sum }]; returns number of values

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symbol()

symbol: Name; pushes context, returns symbol

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then()

then: Then [ [ vars ] stmts ];

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toString()

Represents code as text

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