Count variable occurrences

examples/repl.rs

@@ -4,7 +4,8 @@ use std::sync::atomic::{self, AtomicBool};
 use std::sync::Arc;
 use std::time::Instant;
 
-use logru::ast::{Sym, VarScope};
+use logru::analysis::find_unique_variables;
+use logru::ast::{Rule, Sym, VarScope};
 use logru::resolve::{ArithmeticResolver, ResolverExt};
 use logru::search::{query_dfs, Resolved, Resolver};
 use logru::term_arena::{AppTerm, ArgRange};
@@ -193,6 +194,22 @@ fn query(state: &mut AppState, args: &str) {
     }
 }
 
+fn analyze_rules(rules: &[Rule]) {
+    for rule in rules.iter().filter(|r| r.scope.is_some()) {
+        let orphans = find_unique_variables(&rule)
+            .iter()
+            .filter_map(|var| rule.scope.as_ref().unwrap().get_name(*var))
+            .collect::<Vec<_>>();
+        if !orphans.is_empty() {
+            print!("Some variables appear only once in the rule:");
+            for name in orphans {
+                print!(" {},", name);
+            }
+            println!("\nare those typos?");
+        }
+    }
+}
+
 static COMMANDS: &[Command] = &[
     Command {
         name: ":define",
@@ -203,7 +220,15 @@ static COMMANDS: &[Command] = &[
                 println!("Usage:\n\t:define <source>");
                 return;
             }
-            match state.universe.load_str(args) {
+            let res = state
+                .universe
+                .parse_rules(args)
+                .map(|rules| {
+                    analyze_rules(&rules);
+                    rules
+                })
+                .map(|rules| state.universe.insert_rules(rules));
+            match res {
                 Ok(()) => {
                     println!("Defined!");
                 }
@@ -248,14 +273,24 @@ static COMMANDS: &[Command] = &[
                 return;
             }
             match std::fs::read_to_string(args) {
-                Ok(contents) => match state.universe.load_str(&contents) {
-                    Ok(()) => {
-                        println!("Loaded!");
-                    }
-                    Err(err) => {
-                        println!("Failed to parse: {:?}", err);
+                Ok(contents) => {
+                    let res = state
+                        .universe
+                        .parse_rules(&contents)
+                        .map(|rules| {
+                            analyze_rules(&rules);
+                            rules
+                        })
+                        .map(|rules| state.universe.insert_rules(rules));
+                    match res {
+                        Ok(()) => {
+                            println!("Loaded!");
+                        }
+                        Err(err) => {
+                            println!("Failed to parse: {:?}", err);
+                        }
                     }
-                },
+                }
                 Err(err) => {
                     println!("Failed to load: {}", err);
                 }

src/analysis.rs

@@ -0,0 +1,32 @@
+//! Program analysis proceduress
+
+use crate::ast::{Rule, Term, Var};
+use std::collections::{HashMap, HashSet};
+
+/// Finds variables occuring only once in the rule (together in head and tail).
+pub fn find_unique_variables(rule: &Rule) -> HashSet<Var> {
+    let vars = count_variables(rule);
+    vars.into_iter()
+        .filter(|(_var, count)| *count == 1)
+        .map(|(var, _count)| var)
+        .collect()
+}
+
+/// Counts the number of occurrences of all variables in the rule (both in head and tail).
+pub fn count_variables(rule: &Rule) -> HashMap<Var, usize> {
+    let mut vars = HashMap::new();
+    count_in_args(&mut vars, &rule.head.args);
+    count_in_args(&mut vars, &rule.tail);
+    vars
+}
+
+fn count_in_args(mut vars: &mut HashMap<Var, usize>, args: &[Term]) {
+    for term in args {
+        match term {
+            Term::Var(var) => *vars.entry(*var).or_insert(0) += 1,
+            Term::Int(_) => {}
+            Term::Cut => {}
+            Term::App(appterm) => count_in_args(&mut vars, &appterm.args),
+        }
+    }
+}

src/lib.rs

@@ -152,6 +152,7 @@
 #[cfg(doctest)]
 pub struct ReadmeDoctests;
 
+pub mod analysis;
 pub mod ast;
 pub mod resolve;
 pub mod search;

src/textual.rs

@@ -11,7 +11,7 @@ pub use parser::{ParseError, ParseErrorKind};
 use pretty::ScopedPrettifier;
 
 use crate::{
-    ast::Query,
+    ast::{Query, Rule},
     resolve::RuleResolver,
     search::{self, SolutionIter},
     universe::{RuleSet, SymbolOverlay, SymbolStore},
@@ -91,12 +91,22 @@ impl TextualUniverse {
         }
     }
 
-    /// Load a set of rules from a string.
-    pub fn load_str(&mut self, rules: &str) -> Result<(), ParseError> {
-        let rules = Parser::new(&mut self.symbols).parse_rules_str(rules)?;
+    /// Parse a set of rules using the symbols defined in this universe.
+    pub fn parse_rules(&mut self, rules: &str) -> Result<Vec<Rule>, ParseError> {
+        Parser::new(&mut self.symbols).parse_rules_str(rules)
+    }
+
+    /// Insert rules previously parsed using [`Self::parse_rules`].
+    pub fn insert_rules(&mut self, rules: Vec<Rule>) {
         for rule in rules {
             self.rules.insert(rule);
         }
+    }
+
+    /// Load a set of rules from a string.
+    pub fn load_str(&mut self, rules: &str) -> Result<(), ParseError> {
+        let rules = self.parse_rules(rules)?;
+        self.insert_rules(rules);
         Ok(())
     }