I've been trying out the Ply example calculator from Github.
When I run the calculator, it runs inside of a REPL. How would I use Ply to enable multiple expressions to be evaluated, one after the other.
For example, if I enter 3+4 the REPL does this:
calc > 3+4
7
calc >
If I enter 4+3 6+2 the REPL does this:
calc > 4+3 6+2
Syntax error at '6'
2
calc >
How would I modify the example calculator to enable the REPL to do this:
calc > 4+3 6+2
7
8
calc >
Do I need to modify the grammar, the parser or both? I've tried modifying the grammar to make it left recursive but it doesn't seem to work.
The sample calculator's grammar allows expressions like - 42 (or -(4*8)+7). If such an expression were the second expression on a line, it would create an ambiguity. Is:
calc > 4 * 3 -(4*8)+7
one expression or two?
One way to make the grammar unambiguous would be to allow multiple expressions on a line separated with a comma. You could do that by just adding '.' to the list of literal tokens, and placing the function
def p_line(p):
'''line : statement
| line ',' statement'''
pass
as the first parser function (i.e., just before p_statement_assign.
With that change:
$ python calc.py
Generating LALR tables
calc > 2+3
5
calc > 2+3,4+6
5
10
calc > 2,3
2
3
calc > a=2,a+7
9