用Python撸DSL(领域特定语言)

Code

何为DSL：

DSL就是一种特定解决领域问题的的迷你语言。如SQL语言，正则表达式

内部与外部

指的是实现DSL的方式是否与宿主语言隔离。

内部DSL(Internal DSL)
所谓内部DSL，就是用一种提供语言扩展功能的宿主语言来扩充的。
如Django中的Model

外部DSL(External DSL)
外部DSL则与源语言无关，重头写词法分析器、语法分析器以及解释执行器。

为何要编写DSL

举个例子，一个HTML表格

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<form>
<label>Name:</label><input type=”text” name=”name”/>
<label>Email:</label><input type=”text” name=”email”/>
<label>Password:</label><input type=”password” name=”name”/>
</form>

编写这个HTML文档需要编写者具有HTML的知识
我们尝试着编写自己的DSL，将语句简化为

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UserForm
username:CharField -> label:Username size:25;
email:EmailField -> size:32;
password:PasswordField;

下面我们使用pyparsing库，来制作一款属于自己的DSL语言

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from pyparsing import Word, OneOrMore, Group, Suppress, alphanums, oneOf, alphas, Optional, lineEnd
def convert_prop_to_dict(tokens):
    prop_dict = {}
    for token in tokens:
        prop_dict[token[0]] = token[1]
    return prop_dict
# Suppress 表示不捕获
newline = Suppress(lineEnd)
colon = Suppress(":")
arrow = Suppress("->")
semicolon = Suppress(";")
word = Word(alphas)
key = word
value = Word(alphanums)
field_type = oneOf("CharField EmailField PasswordField")
field_name = word
form_name = word.setResultsName("form_name")
field_property = Group(key + colon + value)
field = Group(field_name + colon + field_type + Optional(arrow + OneOrMore(field_property) + semicolon).setParseAction(
        convert_prop_to_dict))
form = form_name + newline + OneOrMore(field).setResultsName("form_field")
input_form = '''
UserForm
username:CharField -> label:Username size:25;
email:EmailField -> size:32;
password:PasswordField;
'''
'''
External DSL
'''
def get_field_html(field):
    properties = field[2]
    label = properties["label"] if "label" in properties else field[0]
    label_html = "<label>" + label + "</label>"
    attributes = {"name": field[0]}
    attributes.update(properties)
    if field[1] == "CharField" or field[1] == "EmailField":
        attributes["type"] = "text"
    else:
        attributes["type"] = "password"
    if "label" in attributes:
        del attributes["label"]
    attributes_html = " ".join([name + "='" + value + "'" for name, value in attributes.items()])
    field_html = "<input " + attributes_html + "/>"
    return label_html + field_html + "<br/>"
def render(form):
    fields_html = "".join([get_field_html(field) for field in form.form_field])
    return "<form id='" + form.form_name.lower() + "'>" + fields_html + "</form>"
print(render(form.parseString(input_form)))
'''
Internal DSL
'''
class HtmlElement(object):
    default_attributes = {}
    tag = "unknown_tag"
    def __init__(self, *args, **kwargs):
        self.attributes = kwargs
        self.attributes.update(self.default_attributes)
        self.children = args
    def __str__(self):
        attribute_html = " ".join(["{}='{}'".format(name, value)
                                   for name, value in self.attributes.items()])
        if not self.children:
            return "<{} {}/>".format(self.tag, attribute_html)
        else:
            children_html = "".join([str(child) for child in self.children])
            return "<{} {}>{}</{}>".format(self.tag, attribute_html, children_html, self.tag)
# print(HtmlElement(id="test"))
# <unknown_tag id='test'/>
# print (HtmlElement(HtmlElement(name="test"), id="id"))
# <unknown_tag id='id'><unknown_tag name='test'/></unknown_tag>
class InputElement(HtmlElement):
    tag = "input"
    def __init__(self, *args, **kwargs):
        HtmlElement.__init__(self, *args, **kwargs)
        self.label = self.attributes["label"] if "label" in self.attributes else self.attributes["name"]
        if "label" in self.attributes:
            del self.attributes["label"]
    def __str__(self):
        label_html = "<label>{}</label>".format(self.label)
        return label_html + HtmlElement.__str__(self) + "<br/>"
# print(InputElement(name="username"))
# <label>username</label><input name='username'/><br/>
# print(InputElement(name="username", label="User ID"))
# <label>User ID</label><input name='username'/><br/>
class Form(HtmlElement):
    tag = "form"
class CharField(InputElement):
    default_attributes = {"type": "text"}
class EmailField(CharField):
    pass
class PasswordField(InputElement):
    default_attributes = {"type": "password"}
def render(form):
    field_dict = {"CharField": CharField, "EmailField":
        EmailField, "PasswordField": PasswordField}
    fields = [field_dict[field[1]](name=field[0], **field[2]) for field in form.form_field]
    return Form(*fields, id=form.form_name.lower())
print(render(form.parseString(input_form)))

本文标题:用Python撸DSL(领域特定语言)

文章作者:Vincent Zhong

发布时间:2016-10-14, 20:01:26

最后更新:2019-07-07, 13:13:10

原始链接:https://wax8280.github.io/2016/10/14/用Python撸DSL(领域特定语言)/

许可协议: "署名-非商用-相同方式共享 4.0" 转载请保留原文链接及作者。

文章目录
  1. 1. 何为DSL：
  2. 2. 内部与外部
  3. 3. 为何要编写DSL
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