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diff --git a/third_party/python/ply/example/BASIC/basparse.py b/third_party/python/ply/example/BASIC/basparse.py
new file mode 100644
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+++ b/third_party/python/ply/example/BASIC/basparse.py
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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