finished inc and dec, and tests

src/stl.rs

@@ -349,6 +349,28 @@ pub fn static_stdlib(syms: &mut SymTable) -> Result<(), String> {
         },
     );
 
+    syms.insert(
+        "inc".to_string(),
+        Symbol {
+            name: String::from("inc"),
+            args: Args::Lazy(1),
+            conditional_branches: true,
+            docs: math::INC_DOCSTRING.to_string(),
+            value: ValueType::Internal(Rc::new(math::inc_callback)),
+        },
+    );
+
+    syms.insert(
+        "dec".to_string(),
+        Symbol {
+            name: String::from("dec"),
+            args: Args::Lazy(1),
+            conditional_branches: true,
+            docs: math::DEC_DOCSTRING.to_string(),
+            value: ValueType::Internal(Rc::new(math::dec_callback)),
+        },
+    );
+
     Ok(())
 }
 

src/stl/math.rs

@@ -15,7 +15,7 @@
  */
 
 use crate::segment::{Ctr, Seg};
-use crate::sym::SymTable;
+use crate::sym::{SymTable, ValueType};
 
 fn isnumeric(arg: &Ctr) -> bool {
     match arg {
@@ -358,3 +358,77 @@ pub fn islte_callback(ast: &Seg, syms: &mut SymTable) -> Result<Ctr, String> {
         Err("impossible state: islt returned non-bool".to_string())
     }
 }
+
+pub const INC_DOCSTRING: &str = "Accepts a single argument, expects it to be a symbol.
+The symbol is fetched from the symbol table.
+If the symbol is not an integer an error is returned.
+The symbol is redefined as symbol + 1.
+
+This call is similar to the following:
+(def counter '' (add counter 1))
+with the caveat that your docstring is preserved.";
+
+pub fn inc_callback(ast: &Seg, syms: &mut SymTable) -> Result<Ctr, String> {
+    let var_name: String;
+    if let Ctr::Symbol(ref s) = *ast.car {
+        var_name = s.clone();
+    } else {
+        return Err("argument should be a symbol".to_string());
+    }
+
+    let mut sym = syms
+        .remove(&var_name)
+        .expect(&format!("symbol {var_name} is not defined"));
+
+    if let ValueType::VarForm(ref var) = sym.value {
+        if let Ctr::Integer(ref b) = **var {
+            sym.value = ValueType::VarForm(Box::new(Ctr::Integer(b + 1)));
+        } else {
+            syms.insert(var_name, sym);
+            return Err("can only increment an integer".to_string());
+        }
+    } else {
+        syms.insert(var_name, sym);
+        return Err("cannot increment a function".to_string());
+    }
+
+    syms.insert(var_name, sym);
+    Ok(Ctr::None)
+}
+
+pub const DEC_DOCSTRING: &str = "Accepts a single argument, expects it to be a symbol.
+The symbol is fetched from the symbol table.
+If the symbol is not an integer an error is returned.
+The symbol is redefined as symbol - 1.
+
+This call is similar to the following:
+(def counter '' (sub counter 1))
+with the caveat that your docstring is preserved.";
+
+pub fn dec_callback(ast: &Seg, syms: &mut SymTable) -> Result<Ctr, String> {
+    let var_name: String;
+    if let Ctr::Symbol(ref s) = *ast.car {
+        var_name = s.clone();
+    } else {
+        return Err("argument should be a symbol".to_string());
+    }
+
+    let mut sym = syms
+        .remove(&var_name)
+        .expect(&format!("symbol {var_name} is not defined"));
+
+    if let ValueType::VarForm(ref var) = sym.value {
+        if let Ctr::Integer(ref b) = **var {
+            sym.value = ValueType::VarForm(Box::new(Ctr::Integer(b - 1)));
+        } else {
+            syms.insert(var_name, sym);
+            return Err("can only decrement an integer".to_string());
+        }
+    } else {
+        syms.insert(var_name, sym);
+        return Err("cannot decrement a function".to_string());
+    }
+
+    syms.insert(var_name, sym);
+    Ok(Ctr::None)
+}