path: root/example/BASIC/basparse.py

# 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):
    bparser.error = 0
    p = bparser.parse(data)
    if bparser.error: return None
    return p