eqlog 0.9.0

Datalog with equality
Documentation 
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

//! Per-rule "variable occurs at least twice" check. See [`check_occurrences`]
//! for the entry point.

use std::collections::BTreeSet;

use crate::ast::*;
use crate::error::CompileError;
use crate::scopes::{Scopes, Symbol};

/// Walk `ast` rooted at `module` and report the first variable occurrence
/// that is not reachable from (and to) another occurrence of the same name
/// via the scope graph, i.e. the first variable that is used only once in
/// its scope.
pub fn check_occurrences(ast: &Ast, scopes: &Scopes, module: ModuleId) -> Result<(), CompileError> {
    let checker = OccurrencesChecker { ast, scopes };
    checker.check_module(module)
}

struct OccurrencesChecker<'a> {
    ast: &'a Ast,
    scopes: &'a Scopes,
}

impl<'a> OccurrencesChecker<'a> {
    fn check_module(&self, module: ModuleId) -> Result<(), CompileError> {
        for decl in self.ast.module(module).decls.clone() {
            self.check_decl(decl)?;
        }
        Ok(())
    }

    fn check_decl(&self, decl: DeclId) -> Result<(), CompileError> {
        match *self.ast.decl(decl) {
            Decl::Type(_) | Decl::Pred(_) | Decl::Func(_) | Decl::Enum(_) => Ok(()),
            Decl::Rule(id) => self.check_rule(id),
            Decl::Model(id) => {
                for child in self.ast.model_decl(id).body.clone() {
                    self.check_decl(child)?;
                }
                Ok(())
            }
        }
    }

    /// Collect every [`VarTermId`] occurrence in the rule body in source
    /// order, then flag any pair of occurrences that share a name in the
    /// scope graph. An occurrence left unflagged is a singleton use.
    fn check_rule(&self, rule: RuleDeclId) -> Result<(), CompileError> {
        let mut occurrences: Vec<VarTermId> = Vec::new();
        for stmt in self.ast.rule_decl(rule).body.clone() {
            self.collect_stmt(stmt, &mut occurrences);
        }

        let mut used_twice: BTreeSet<VarTermId> = BTreeSet::new();
        for &v in &occurrences {
            let name = &self.ast.var_term(v).name;
            let entry = self.scopes.entry(v);
            if let Some(Symbol::Var(prev)) = self.scopes.lookup(entry, name) {
                used_twice.insert(v);
                used_twice.insert(prev);
            }
        }

        match occurrences.into_iter().find(|v| !used_twice.contains(v)) {
            Some(v) => Err(CompileError::VariableOccursOnlyOnce {
                name: self.ast.var_term(v).name.clone(),
                location: self.ast.loc(v),
            }),
            None => Ok(()),
        }
    }

    fn collect_stmt(&self, stmt: StmtId, occ: &mut Vec<VarTermId>) {
        match *self.ast.stmt(stmt) {
            Stmt::If(id) => self.collect_if_atom(self.ast.if_stmt(id).atom, occ),
            Stmt::Then(id) => self.collect_then_atom(self.ast.then_stmt(id).atom, occ),
            Stmt::Branch(id) => {
                for block in self.ast.branch_stmt(id).blocks.clone() {
                    for s in &block {
                        self.collect_stmt(*s, occ);
                    }
                }
            }
            Stmt::Match(id) => {
                let MatchStmt { term, cases } = self.ast.match_stmt(id);
                let term = *term;
                let cases = cases.clone();
                self.collect_term(term, occ);
                for case in &cases {
                    let MatchCase { pattern, body } = self.ast.match_case(*case);
                    let pattern = *pattern;
                    let body = body.clone();
                    self.collect_term(pattern, occ);
                    for s in &body {
                        self.collect_stmt(*s, occ);
                    }
                }
            }
        }
    }

    fn collect_if_atom(&self, atom: IfAtomId, occ: &mut Vec<VarTermId>) {
        match *self.ast.if_atom(atom) {
            IfAtom::Equal(id) => {
                let EqualAtom { lhs, rhs } = *self.ast.equal_atom(id);
                self.collect_term(lhs, occ);
                self.collect_term(rhs, occ);
            }
            IfAtom::Defined(id) => {
                let DefinedIfAtom { term } = *self.ast.defined_if_atom(id);
                self.collect_term(term, occ);
            }
            IfAtom::Pred(id) => {
                let PredAtom { pred, args } = *self.ast.pred_atom(id);
                self.collect_pred_expr(pred, occ);
                self.collect_term_list(args, occ);
            }
            IfAtom::Var(id) => {
                let VarIfAtom { term, typ } = *self.ast.var_if_atom(id);
                self.collect_type_expr(typ, occ);
                self.collect_term(term, occ);
            }
        }
    }

    fn collect_then_atom(&self, atom: ThenAtomId, occ: &mut Vec<VarTermId>) {
        match *self.ast.then_atom(atom) {
            ThenAtom::Equal(id) => {
                let EqualAtom { lhs, rhs } = *self.ast.equal_atom(id);
                self.collect_term(lhs, occ);
                self.collect_term(rhs, occ);
            }
            ThenAtom::Defined(id) => {
                let DefinedThenAtom { var, term } = *self.ast.defined_then_atom(id);
                if let Some(v) = var {
                    self.collect_term(v, occ);
                }
                self.collect_term(term, occ);
            }
            ThenAtom::Pred(id) => {
                let PredAtom { pred, args } = *self.ast.pred_atom(id);
                self.collect_pred_expr(pred, occ);
                self.collect_term_list(args, occ);
            }
        }
    }

    fn collect_term(&self, term: TermId, occ: &mut Vec<VarTermId>) {
        match *self.ast.term(term) {
            Term::Var(id) => occ.push(id),
            Term::Wildcard => {}
            Term::App(id) => {
                let AppTerm { func, args } = *self.ast.app_term(id);
                self.collect_func_expr(func, occ);
                self.collect_term_list(args, occ);
            }
            Term::Dom(id) => self.collect_term(self.ast.dom_term(id).arg, occ),
            Term::Cod(id) => self.collect_term(self.ast.cod_term(id).arg, occ),
            Term::MorApp(id) => {
                let MorAppTerm { mor, arg } = *self.ast.mor_app_term(id);
                self.collect_term(mor, occ);
                self.collect_term(arg, occ);
            }
        }
    }

    fn collect_term_list(&self, list: TermListId, occ: &mut Vec<VarTermId>) {
        for term in self.ast.term_list(list).terms.clone() {
            self.collect_term(term, occ);
        }
    }

    fn collect_type_expr(&self, type_expr: TypeExprId, occ: &mut Vec<VarTermId>) {
        match *self.ast.type_expr(type_expr) {
            TypeExpr::Ambient(_) | TypeExpr::Mor(_) => {}
            TypeExpr::Member(id) => self.collect_term(self.ast.member_type_expr(id).term, occ),
        }
    }

    fn collect_pred_expr(&self, pred_expr: PredExprId, occ: &mut Vec<VarTermId>) {
        match *self.ast.pred_expr(pred_expr) {
            PredExpr::Ambient(_) => {}
            PredExpr::Member(id) => self.collect_term(self.ast.member_pred_expr(id).term, occ),
        }
    }

    fn collect_func_expr(&self, func_expr: FuncExprId, occ: &mut Vec<VarTermId>) {
        match *self.ast.func_expr(func_expr) {
            FuncExpr::Ambient(_) => {}
            FuncExpr::Member(id) => self.collect_term(self.ast.member_func_expr(id).term, occ),
        }
    }
}