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# An implementation of Dartmouth BASIC (1964)
#
from ply import *
import basiclex
tokens = basiclex.tokens
precedence = (
('left', 'PLUS','MINUS'),
('left', 'TIMES','DIVIDE'),
('left', 'POWER'),
('right','UMINUS')
)
#### A BASIC program is a series of statements. We represent the program as a
#### dictionary of tuples indexed by line number.
def p_program(p):
'''program : program statement
| statement'''
if len(p) == 2 and p[1]:
p[0] = { }
line,stat = p[1]
p[0][line] = stat
elif len(p) ==3:
p[0] = p[1]
if not p[0]: p[0] = { }
if p[2]:
line,stat = p[2]
p[0][line] = stat
#### This catch-all rule is used for any catastrophic errors. In this case,
#### we simply return nothing
def p_program_error(p):
'''program : error'''
p[0] = None
p.parser.error = 1
#### Format of all BASIC statements.
def p_statement(p):
'''statement : INTEGER command NEWLINE'''
if isinstance(p[2],str):
print("%s %s %s" % (p[2],"AT LINE", p[1]))
p[0] = None
p.parser.error = 1
else:
lineno = int(p[1])
p[0] = (lineno,p[2])
#### Interactive statements.
def p_statement_interactive(p):
'''statement : RUN NEWLINE
| LIST NEWLINE
| NEW NEWLINE'''
p[0] = (0, (p[1],0))
#### Blank line number
def p_statement_blank(p):
'''statement : INTEGER NEWLINE'''
p[0] = (0,('BLANK',int(p[1])))
#### Error handling for malformed statements
def p_statement_bad(p):
'''statement : INTEGER error NEWLINE'''
print("MALFORMED STATEMENT AT LINE %s" % p[1])
p[0] = None
p.parser.error = 1
#### Blank line
def p_statement_newline(p):
'''statement : NEWLINE'''
p[0] = None
#### LET statement
def p_command_let(p):
'''command : LET variable EQUALS expr'''
p[0] = ('LET',p[2],p[4])
def p_command_let_bad(p):
'''command : LET variable EQUALS error'''
p[0] = "BAD EXPRESSION IN LET"
#### READ statement
def p_command_read(p):
'''command : READ varlist'''
p[0] = ('READ',p[2])
def p_command_read_bad(p):
'''command : READ error'''
p[0] = "MALFORMED VARIABLE LIST IN READ"
#### DATA statement
def p_command_data(p):
'''command : DATA numlist'''
p[0] = ('DATA',p[2])
def p_command_data_bad(p):
'''command : DATA error'''
p[0] = "MALFORMED NUMBER LIST IN DATA"
#### PRINT statement
def p_command_print(p):
'''command : PRINT plist optend'''
p[0] = ('PRINT',p[2],p[3])
def p_command_print_bad(p):
'''command : PRINT error'''
p[0] = "MALFORMED PRINT STATEMENT"
#### Optional ending on PRINT. Either a comma (,) or semicolon (;)
def p_optend(p):
'''optend : COMMA
| SEMI
|'''
if len(p) == 2:
p[0] = p[1]
else:
p[0] = None
#### PRINT statement with no arguments
def p_command_print_empty(p):
'''command : PRINT'''
p[0] = ('PRINT',[],None)
#### GOTO statement
def p_command_goto(p):
'''command : GOTO INTEGER'''
p[0] = ('GOTO',int(p[2]))
def p_command_goto_bad(p):
'''command : GOTO error'''
p[0] = "INVALID LINE NUMBER IN GOTO"
#### IF-THEN statement
def p_command_if(p):
'''command : IF relexpr THEN INTEGER'''
p[0] = ('IF',p[2],int(p[4]))
def p_command_if_bad(p):
'''command : IF error THEN INTEGER'''
p[0] = "BAD RELATIONAL EXPRESSION"
def p_command_if_bad2(p):
'''command : IF relexpr THEN error'''
p[0] = "INVALID LINE NUMBER IN THEN"
#### FOR statement
def p_command_for(p):
'''command : FOR ID EQUALS expr TO expr optstep'''
p[0] = ('FOR',p[2],p[4],p[6],p[7])
def p_command_for_bad_initial(p):
'''command : FOR ID EQUALS error TO expr optstep'''
p[0] = "BAD INITIAL VALUE IN FOR STATEMENT"
def p_command_for_bad_final(p):
'''command : FOR ID EQUALS expr TO error optstep'''
p[0] = "BAD FINAL VALUE IN FOR STATEMENT"
def p_command_for_bad_step(p):
'''command : FOR ID EQUALS expr TO expr STEP error'''
p[0] = "MALFORMED STEP IN FOR STATEMENT"
#### Optional STEP qualifier on FOR statement
def p_optstep(p):
'''optstep : STEP expr
| empty'''
if len(p) == 3:
p[0] = p[2]
else:
p[0] = None
#### NEXT statement
def p_command_next(p):
'''command : NEXT ID'''
p[0] = ('NEXT',p[2])
def p_command_next_bad(p):
'''command : NEXT error'''
p[0] = "MALFORMED NEXT"
#### END statement
def p_command_end(p):
'''command : END'''
p[0] = ('END',)
#### REM statement
def p_command_rem(p):
'''command : REM'''
p[0] = ('REM',p[1])
#### STOP statement
def p_command_stop(p):
'''command : STOP'''
p[0] = ('STOP',)
#### DEF statement
def p_command_def(p):
'''command : DEF ID LPAREN ID RPAREN EQUALS expr'''
p[0] = ('FUNC',p[2],p[4],p[7])
def p_command_def_bad_rhs(p):
'''command : DEF ID LPAREN ID RPAREN EQUALS error'''
p[0] = "BAD EXPRESSION IN DEF STATEMENT"
def p_command_def_bad_arg(p):
'''command : DEF ID LPAREN error RPAREN EQUALS expr'''
p[0] = "BAD ARGUMENT IN DEF STATEMENT"
#### GOSUB statement
def p_command_gosub(p):
'''command : GOSUB INTEGER'''
p[0] = ('GOSUB',int(p[2]))
def p_command_gosub_bad(p):
'''command : GOSUB error'''
p[0] = "INVALID LINE NUMBER IN GOSUB"
#### RETURN statement
def p_command_return(p):
'''command : RETURN'''
p[0] = ('RETURN',)
#### DIM statement
def p_command_dim(p):
'''command : DIM dimlist'''
p[0] = ('DIM',p[2])
def p_command_dim_bad(p):
'''command : DIM error'''
p[0] = "MALFORMED VARIABLE LIST IN DIM"
#### List of variables supplied to DIM statement
def p_dimlist(p):
'''dimlist : dimlist COMMA dimitem
| dimitem'''
if len(p) == 4:
p[0] = p[1]
p[0].append(p[3])
else:
p[0] = [p[1]]
#### DIM items
def p_dimitem_single(p):
'''dimitem : ID LPAREN INTEGER RPAREN'''
p[0] = (p[1],eval(p[3]),0)
def p_dimitem_double(p):
'''dimitem : ID LPAREN INTEGER COMMA INTEGER RPAREN'''
p[0] = (p[1],eval(p[3]),eval(p[5]))
#### Arithmetic expressions
def p_expr_binary(p):
'''expr : expr PLUS expr
| expr MINUS expr
| expr TIMES expr
| expr DIVIDE expr
| expr POWER expr'''
p[0] = ('BINOP',p[2],p[1],p[3])
def p_expr_number(p):
'''expr : INTEGER
| FLOAT'''
p[0] = ('NUM',eval(p[1]))
def p_expr_variable(p):
'''expr : variable'''
p[0] = ('VAR',p[1])
def p_expr_group(p):
'''expr : LPAREN expr RPAREN'''
p[0] = ('GROUP',p[2])
def p_expr_unary(p):
'''expr : MINUS expr %prec UMINUS'''
p[0] = ('UNARY','-',p[2])
#### Relational expressions
def p_relexpr(p):
'''relexpr : expr LT expr
| expr LE expr
| expr GT expr
| expr GE expr
| expr EQUALS expr
| expr NE expr'''
p[0] = ('RELOP',p[2],p[1],p[3])
#### Variables
def p_variable(p):
'''variable : ID
| ID LPAREN expr RPAREN
| ID LPAREN expr COMMA expr RPAREN'''
if len(p) == 2:
p[0] = (p[1],None,None)
elif len(p) == 5:
p[0] = (p[1],p[3],None)
else:
p[0] = (p[1],p[3],p[5])
#### Builds a list of variable targets as a Python list
def p_varlist(p):
'''varlist : varlist COMMA variable
| variable'''
if len(p) > 2:
p[0] = p[1]
p[0].append(p[3])
else:
p[0] = [p[1]]
#### Builds a list of numbers as a Python list
def p_numlist(p):
'''numlist : numlist COMMA number
| number'''
if len(p) > 2:
p[0] = p[1]
p[0].append(p[3])
else:
p[0] = [p[1]]
#### A number. May be an integer or a float
def p_number(p):
'''number : INTEGER
| FLOAT'''
p[0] = eval(p[1])
#### A signed number.
def p_number_signed(p):
'''number : MINUS INTEGER
| MINUS FLOAT'''
p[0] = eval("-"+p[2])
#### List of targets for a print statement
#### Returns a list of tuples (label,expr)
def p_plist(p):
'''plist : plist COMMA pitem
| pitem'''
if len(p) > 3:
p[0] = p[1]
p[0].append(p[3])
else:
p[0] = [p[1]]
def p_item_string(p):
'''pitem : STRING'''
p[0] = (p[1][1:-1],None)
def p_item_string_expr(p):
'''pitem : STRING expr'''
p[0] = (p[1][1:-1],p[2])
def p_item_expr(p):
'''pitem : expr'''
p[0] = ("",p[1])
#### Empty
def p_empty(p):
'''empty : '''
#### Catastrophic error handler
def p_error(p):
if not p:
print("SYNTAX ERROR AT EOF")
bparser = yacc.yacc()
def parse(data,debug=0):
bparser.error = 0
p = bparser.parse(data,debug=debug)
if bparser.error: return None
return p
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