The Book

Class: Functions04

Seven~ Functions04

Example 7/04: compile parameter-less functions into stack machine code.

new Functions04()

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Extends

Classes

Fun
Symbol
Var

Members

funct

Describes current function

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size

Manages next (global) variable address

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Methods

Do()

Do: 'do'; returns address of slot for bzero to od

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Else()

Else: 'else'; creates slot for branch to fi, returns address of else

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Then()

Then: 'then'; returns address for bzero to else fi

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While()

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

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_alloc()

Returns new Var at next global address.

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_check_defs()

Flags undefined functions, returns main if defined

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_dcl()

(Re-)defines and returns sym, cannot be undefined

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_find()

Returns symbol description for name, if any

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_startup(main)

Generates Call to main.start and Print result

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Name Type Description
main Fun

describes main().
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add()

add: '+' product;

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assign()

assign: Name [ '=' sum ];

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divide()

divide: '/' signed;

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eq()

eq: '=' sum;

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fun()

fun: head [ 'begin' stmts 'end' ] ';';

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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 stmts 'od';

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lt()

lt: '<' sum;

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multiply()

multiply: '*' signed;

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name()

name: Name;

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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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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 stmts [ Else stmts ] '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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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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toString()

Represents code as text

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