134 lines
3.4 KiB
Python
134 lines
3.4 KiB
Python
from keywords import Atom
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"""
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The grammar is defined by the following constructs:
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The top level object is called GRAMMAR, which is the grammar for a class. It is a list object.
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Inside this list, each element can be any of the following:
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- a token (denoted by a Keyword enum)
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- a bitwise mask of the Keyword enum to denote multiple possibilities
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- Another list, to denote zero-or-more of a inner-sequence
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- A tuple, to denote zero-or-one of a inner-sequence
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- A lambda denotes a non-terminal part of the grammar
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This is basically an attempt to translate Figure 10.5 from the book into
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a Python structure.
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"""
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class Element:
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def __init__(self, name, grammar):
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self.name = name
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self.grammar = grammar
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TYPES = Element('type', Atom.INT | Atom.CHAR | Atom.BOOLEAN | Atom.IDENTIFIER)
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CLASSVARDEC = Element('classVarDec', [
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# static|field type (, name)* ;
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Atom.STATIC | Atom.FIELD,
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TYPES,
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[Atom.COMMA, Atom.IDENTIFIER],
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Atom.SEMICOLON
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])
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VARDEC = Element('varDec', [Atom.VAR, TYPES, Atom.IDENTIFIER,
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[Atom.COMMA, Atom.IDENTIFIER],
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Atom.SEMICOLON
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])
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UNARY_OP = Element('unaryOp', Atom.NOT | Atom.MINUS)
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CONSTANT = Element('KeywordConstant', Atom.TRUE | Atom.FALSE|Atom.NULL|Atom.THIS)
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TERM = Element('term', Atom.INTEGERCONSTANT | Atom.STRINGCONSTANT | Atom.TRUE | Atom.FALSE | Atom.IDENTIFIER)
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OP = Element('op', Atom.PLUS | Atom.MINUS | Atom.MUL | Atom.DIV | Atom.AND | Atom.OR | Atom.GT | Atom.LT | Atom.EQ)
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EXPRESSION = Element('expression', [TERM, [OP, TERM]])
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EXPRESSIONLIST = Element('expressionList', (EXPRESSION, [Atom.COMMA, EXPRESSION]))
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SUBROUTINE_CALL = Element('subroutineCall', {
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(Atom.IDENTIFIER, Atom.PARAN_OPEN): [
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EXPRESSIONLIST,
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Atom.PARAN_CLOSE,
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],
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(Atom.IDENTIFIER, Atom.DOT): [
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Atom.IDENTIFIER,
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Atom.PARAN_OPEN,
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EXPRESSIONLIST,
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Atom.PARAN_CLOSE
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]
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})
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STATEMENT = Element('statement', {
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(Atom.LET): [Atom.IDENTIFIER, (Atom.SQUARE_OPEN, EXPRESSION, Atom.SQUARE_CLOSE)],
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(Atom.IF): [
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Atom.PARAN_OPEN,
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EXPRESSION,
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Atom.PARAN_CLOSE,
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Atom.BRACE_OPEN,
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lambda: STATEMENTS,
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Atom.BRACE_CLOSE,
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# This is the tricky one
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( Atom.ELSE, Atom.BRACE_OPEN, lambda:STATEMENT, Atom.BRACE_CLOSE)
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],
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(Atom.WHILE): [
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Atom.PARAN_OPEN,
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EXPRESSION,
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Atom.PARAN_CLOSE,
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Atom.BRACE_OPEN,
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lambda: STATEMENTS,
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Atom.BRACE_CLOSE,
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],
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(Atom.DO): SUBROUTINE_CALL,
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(Atom.RETURN): [(EXPRESSION), Atom.SEMICOLON]
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})
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STATEMENTS = Element('statements', [STATEMENT])
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SUBROUTINE_BODY = Element('subroutineBody', [
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# One or more variable declarations
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# `var type varName (, varName)* ;`
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[VARDEC],
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STATEMENTS
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])
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""" Pseudo-element to help define subroutine declarations """
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RETURN_TYPES= Atom.INT | Atom.CHAR|Atom.BOOLEAN|Atom.IDENTIFIER|Atom.VOID
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# Parameter List =
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# (
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# (type varName) (, type varName)*
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# )?
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# we use tuples for zero OR one of a sequence
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PARAMETER_LIST = Element('parameterList', (
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TYPES,
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Atom.IDENTIFIER,
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[Atom.COMMA, TYPES, Atom.IDENTIFIER]
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))
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SUBROUTINEDEC = Element('subroutineDec', [
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# (constructor | function | method) (void | type) subRoutineName '(' parameterList ')'
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# subroutineBody
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Atom.CONSTRUCTOR | Atom.FUNCTION | Atom.METHOD,
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RETURN_TYPES,
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Atom.IDENTIFIER,
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Atom.PARAN_OPEN,
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PARAMETER_LIST,
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Atom.PARAN_CLOSE,
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# Subroutine Body
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Atom.BRACE_OPEN,
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SUBROUTINE_BODY,
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Atom.BRACE_CLOSE,
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])
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CLASS = Element('class', [
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Atom.CLASS,
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Atom.IDENTIFIER,
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Atom.BRACE_OPEN,
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[CLASSVARDEC],
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[SUBROUTINEDEC],
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Atom.BRACE_CLOSE
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])
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