1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
use std::{
convert::TryFrom,
collections::HashSet,
};
use crate::common::span::{Span, Spanned};
use crate::compiler::{
rule::Rule,
ast::{AST, ASTPattern, ArgPat},
cst::{CST, CSTPattern},
syntax::Syntax
};
pub fn desugar(ast: Spanned<AST>) -> Result<Spanned<CST>, Syntax> {
let mut transformer = Transformer::new();
let cst = transformer.walk(ast)?;
return Ok(cst);
}
pub struct Transformer {
rules: Vec<Spanned<Rule>>,
}
impl Transformer {
pub fn new() -> Transformer {
Transformer { rules: vec![] }
}
pub fn walk(&mut self, ast: Spanned<AST>) -> Result<Spanned<CST>, Syntax> {
let cst: CST = match ast.item {
AST::Symbol(_) => self.symbol(ast.clone())?,
AST::Data(d) => CST::Data(d),
AST::Block(b) => self.block(b)?,
AST::Form(f) => self.form(f)?,
AST::Composition { argument, function } => self.composition(*argument, *function)?,
AST::Pattern(_) => return Err(Syntax::error("Unexpected pattern", &ast.span)),
AST::ArgPat(_) => return Err(Syntax::error("Unexpected argument pattern", &ast.span)),
AST::Syntax { arg_pat, expression } => self.rule(*arg_pat, *expression)?,
AST::Assign { pattern, expression } => self.assign(*pattern, *expression)?,
AST::Lambda { pattern, expression } => self.lambda(*pattern, *expression)?,
AST::Print(e) => CST::Print(Box::new(self.walk(*e)?)),
AST::Label(n, e) => CST::Label(n, Box::new(self.walk(*e)?)),
};
return Ok(Spanned::new(cst, ast.span))
}
pub fn symbol(&mut self, ast: Spanned<AST>) -> Result<CST, Syntax> {
self.form(vec![ast])
}
pub fn call(&mut self, mut f: Vec<Spanned<AST>>) -> Result<CST, Syntax> {
match f.len() {
0 => unreachable!("A call must have at least two values - a function and an expression"),
1 => match f.pop().unwrap().item {
AST::Symbol(name) => Ok(CST::Symbol(name)),
_ => unreachable!("A non-symbol call of length 1 is can not be constructed")
},
2 => {
let arg = f.pop().unwrap();
let fun = f.pop().unwrap();
Ok(CST::call(self.walk(fun)?, self.walk(arg)?))
},
_higher => {
let arg = self.walk(f.pop().unwrap())?;
let f_span = Span::join(f.iter().map(|e| e.span.clone()).collect::<Vec<Span>>());
Ok(CST::call(Spanned::new(self.call(f)?, f_span), arg))
},
}
}
pub fn form(&mut self, form: Vec<Spanned<AST>>) -> Result<CST, Syntax> {
let mut keywords = HashSet::new();
for rule in self.rules.iter() {
for keyword in Rule::keywords(&rule.item.arg_pat) {
keywords.insert(keyword);
}
}
let mut matches = vec![];
for rule in self.rules.iter() {
let mut reversed_remaining = form.clone().into_iter().rev().collect();
let possibility = Rule::bind(&rule.item.arg_pat, &mut reversed_remaining);
if let Some(bindings) = possibility {
if reversed_remaining.is_empty() {
matches.push((rule, bindings?))
}
}
}
if matches.len() == 0 { return self.call(form); }
if matches.len() > 1 {
return Err(Syntax::error(
&format!(
"This form matched multiple macros:\n\n{}\
Note: A form may only match one macro, this must be unambiguious;\n\
Try using variable names different than those of pseudokeywords currently in scope,\n\
Adjusting the definitions of locally-defined macros,\n\
or using parenthesis '( ... )' or curlies '{{ ... }}' to group nested macros",
matches.iter()
.map(|s| format!("{}", s.0.span))
.collect::<Vec<String>>()
.join(""),
),
&Spanned::build(&form),
))
}
let (rule, mut bindings) = matches.pop().unwrap();
let expanded = Rule::expand(rule.item.tree.clone(), &mut bindings)?;
return Ok(self.walk(expanded)?.item);
}
pub fn composition(&mut self, argument: Spanned<AST>, function: Spanned<AST>) -> Result<CST, Syntax> {
Ok(CST::call(self.walk(function)?, self.walk(argument)?))
}
pub fn block(&mut self, b: Vec<Spanned<AST>>) -> Result<CST, Syntax> {
let mut expressions = vec![];
for e in b {
expressions.push(self.walk(e)?)
}
Ok(CST::Block(expressions))
}
pub fn assign(&mut self, p: Spanned<ASTPattern>, e: Spanned<AST>) -> Result<CST, Syntax> {
let p_span = p.span.clone();
Ok(CST::assign(
p.map(CSTPattern::try_from)
.map_err(|err| Syntax::error(&err, &p_span))?,
self.walk(e)?
))
}
pub fn lambda(&mut self, p: Spanned<ASTPattern>, e: Spanned<AST>) -> Result<CST, Syntax> {
let p_span = p.span.clone();
let arguments = if let ASTPattern::Chain(c) = p.item { c } else { vec![p] };
let mut expression = self.walk(e)?;
for argument in arguments.into_iter().rev() {
let pattern = argument.map(CSTPattern::try_from)
.map_err(|err| Syntax::error(&err, &p_span))?;
let combined = Span::combine(&pattern.span, &expression.span);
expression = Spanned::new(CST::lambda(pattern, expression), combined);
}
return Ok(expression.item);
}
pub fn rule(&mut self, arg_pat: Spanned<ArgPat>, tree: Spanned<AST>) -> Result<CST, Syntax> {
let patterns_span = arg_pat.span.clone();
let rule = Rule::new(arg_pat, tree)?;
self.rules.push(Spanned::new(rule, patterns_span));
Ok(CST::Block(vec![]))
}
}