Grammar Definition¶

Guide to defining grammars in Grammar School Python.

Default Grammar¶

Grammar School provides a default grammar that supports:

Function calls: greet(name="Alice")
Method chaining: track().add_clip()
Named arguments: func(name="value", count=2)
Positional arguments: func("value", 2)
Various value types: numbers, strings, identifiers, booleans

Using the Default Grammar¶

from grammar_school import Grammar, method

class MyDSL(Grammar):
    @method
    def greet(self, name):
        print(f"Hello, {name}!")

dsl = MyDSL()  # Uses default grammar

Custom Grammar¶

You can provide a custom grammar string:

custom_grammar = """
start: call_chain

call_chain: call ('.' call)*
call: IDENTIFIER "(" args? ")"
args: arg (',' arg)*
arg: IDENTIFIER "=" value | value
value: NUMBER | STRING | IDENTIFIER | BOOL

IDENTIFIER: /[a-zA-Z_][a-zA-Z0-9_]*/
NUMBER: /-?\\d+(\\.\\d+)?/
STRING: /"([^"\\\\]|\\\\.)*"|'([^'\\\\]|\\\\.)*'/
BOOL: "true" | "false"
"""

class MyDSL(Grammar):
    @method
    def greet(self, name):
        print(f"Hello, {name}!")

dsl = MyDSL(grammar=custom_grammar)

Grammar Rules with @rule Decorator¶

For advanced use cases, you can use the @rule decorator:

from grammar_school import rule

@rule("call_chain: call ('.' call)*")
class MyDSL(Grammar):
    @method
    def greet(self, name):
        print(f"Hello, {name}!")

Grammar Syntax¶

Grammar School uses Lark for parsing, which supports:

EBNF-style rules
Regular expressions for terminals
Operator precedence
Ambiguity resolution

See the Lark documentation for complete grammar syntax.