Doesn't compile, but I have a mess.

src/peano.c

@@ -25,35 +25,163 @@
 #include "real.h"
 #include "stack.h"
 
-/**
+long double to_long_double( struct cons_pointer arg );
- * Internal guts of add. Dark and mysterious.
+long int to_long_int( struct stack_frame *frame, struct cons_pointer arg );
- */
+
-struct cons_pointer add_accumulate( struct cons_pointer arg,
+
-                                    struct stack_frame *frame,
+bool zerop( struct cons_pointer arg ) {
-                                    long int *i_accumulator,
+    bool result = false;
-                                    long double *d_accumulator, int *is_int ) {
-    struct cons_pointer result = NIL;
     struct cons_space_object cell = pointer2cell( arg );
 
     switch ( cell.tag.value ) {
         case INTEGERTV:
-            ( *i_accumulator ) += cell.payload.integer.value;
+            result = cell.payload.integer.value == 0;
-            ( *d_accumulator ) += numeric_value( arg );
+            break;
+        case RATIOTV:
+            result = zerop( cell.payload.ratio.dividend );
             break;
         case REALTV:
-            ( *d_accumulator ) += cell.payload.real.value;
+            result = ( cell.payload.real.value == 0 );
-            ( *is_int ) &= false;
             break;
-        case EXCEPTIONTV:
+    }
-            result = arg;
+
+    return result;
+}
+
+/**
+ * TODO: cannot throw an exception out of here, which is a problem
+ * if a ratio may legally have zero as a divisor, or something which is
+ * not a number is passed in.
+ */
+long double to_long_double( struct cons_pointer arg ) {
+    long double result = NAN;   /* not a number, as a long double */
+    struct cons_space_object cell = pointer2cell( arg );
+
+    switch ( cell.tag.value ) {
+        case INTEGERTV:
+            result = cell.payload.integer.value * 1.0;
+        case RATIOTV:
+            {
+                struct cons_space_object dividend =
+                    pointer2cell( cell.payload.ratio.dividend );
+                struct cons_space_object divisor =
+                    pointer2cell( cell.payload.ratio.divisor );
+
+                result =
+                    dividend.payload.integer.value /
+                    divisor.payload.integer.value;
+            }
+            break;
+        case REALTV:
+            result = cell.payload.real.value;
+            break;
+    }
+
+    return result;
+}
+
+
+/**
+ * TODO: cannot throw an exception out of here, which is a problem
+ * if a ratio may legally have zero as a divisor, or something which is
+ * not a number (or is a big number) is passed in.
+ */
+long int to_long_int( struct stack_frame *frame, struct cons_pointer arg ) {
+    long int result = 0;
+    struct cons_space_object cell = pointer2cell( arg );
+    switch ( cell.tag.value ) {
+        case INTEGERTV:
+            result = cell.payload.integer.value;
+            break;
+        case RATIOTV:
+            result = lroundl( to_long_double( arg ) );
+            break;
+        case REALTV:
+            result = lroundl( cell.payload.real.value );
             break;
-        default:
-            result = lisp_throw( c_string_to_lisp_string
-                                 ( "Cannot multiply: not a number" ), frame );
     }
     return result;
 }
 
+long int greatest_common_divisor( long int m, long int n ) {
+    int o;
+    while ( m ) {
+        o = m;
+        m = n % m;
+        n = o;
+    }
+
+    return o;
+}
+
+long int least_common_multiplier( long int m, long int n ) {
+    return m / greatest_common_divisor( m, n ) * n;
+}
+
+/**
+* return a cons_pointer indicating a number which is the sum of
+* the numbers indicated by `arg1` and `arg2`.
+*/
+struct cons_pointer add_2( struct stack_frame *frame, struct cons_pointer arg1,
+                           struct cons_pointer arg2 ) {
+    struct cons_pointer result;
+    struct cons_space_object cell1 = pointer2cell( arg1 );
+    struct cons_space_object cell2 = pointer2cell( arg2 );
+
+    if ( zerop( arg1 ) ) {
+        result = arg2;
+    } else if ( zerop( arg2 ) ) {
+        result = arg1;
+    } else {
+
+        switch ( cell1.tag.value ) {
+            case EXCEPTIONTV:
+                result = cell1;
+                break;
+            case INTEGERTV:
+                switch ( cell2.tag.value ) {
+                    case EXCEPTIONTV:
+                        result = cell2;
+                        break;
+                    case INTEGERTV:
+                        make_integer( cell1.payload.integer.value +
+                                      cell2.payload.integer.value );
+                        break;
+                    case RATIOTV:
+                        result = add_integer_ratio( arg1, arg2 );
+                        break;
+                    case REALTV:
+                        result =
+                            make_real( cell1.payload.integer.value +
+                                       cell2.payload.real.value );
+                        break;
+                    default:
+                        result = lisp_throw( c_string_to_lisp_string
+                                             ( "Cannot add: not a number" ),
+                                             frame );
+                }
+                break;
+            case RATIOTV:
+                switch ( cell2.tag.value ) {
+                    case EXCEPTIONTV:
+                        result = cell2;
+                        break;
+                    case INTEGERTV:
+                        result = add_integer_ratio( arg1, arg2 );
+                        break;
+                    case RATIOTV:
+                        break;
+                    case REALTV:
+                        result =
+                            make_real( cell2.payload.real.value +
+                                       ratio_to_long_double( arg1 ) );
+                        break;
+                }
+        }
+    }
+
+    return result;
+}
 
 /**
  * Add an indefinite number of numbers together
@@ -61,48 +189,38 @@ struct cons_pointer add_accumulate( struct cons_pointer arg,
  * @param frame the stack frame.
  * @return a pointer to an integer or real.
  */
-struct cons_pointer
+struct cons_pointer lisp_add( struct stack_frame
-lisp_add( struct stack_frame *frame, struct cons_pointer env ) {
+                              *frame, struct
+                              cons_pointer env ) {
     struct cons_pointer result = NIL;
-    long int i_accumulator = 0;
+    struct cons_pointer result = make_integer( 0 );
-    long double d_accumulator = 0;
-    int is_int = true;
-
     for ( int i = 0; i < args_in_frame && !nilp( frame->arg[i] ); i++ ) {
-        result =
+        result = add_q( frame, result, frame->arg[i] );
-            add_accumulate( frame->arg[i], frame, &i_accumulator,
-                            &d_accumulator, &is_int );
     }
 
     struct cons_pointer more = frame->more;
-
     while ( consp( more ) ) {
-        result =
+        result = add_2( frame, result, c _car( more ) );
-            add_accumulate( c_car( more ), frame, &i_accumulator,
-                            &d_accumulator, &is_int );
         more = c_cdr( more );
     }
 
-    if ( is_int ) {
-        result = make_integer( i_accumulator );
-    } else {
-        result = make_real( d_accumulator );
-    }
-
     return result;
 }
 
 /**
  * Internal guts of multiply. Dark and mysterious.
  */
-struct cons_pointer multiply_accumulate( struct cons_pointer arg,
+struct cons_pointer multiply_accumulate( struct
-                                         struct stack_frame *frame,
+                                         cons_pointer arg, struct
-                                         long int *i_accumulator,
+                                         stack_frame
-                                         long double *d_accumulator,
+                                         *frame, long
-                                         int *is_int ) {
+                                         int
+                                         *i_accumulator, long
+                                         double
+                                         *d_accumulator, int
+                                         *is_int ) {
     struct cons_pointer result = NIL;
     struct cons_space_object cell = pointer2cell( arg );
-
     switch ( cell.tag.value ) {
         case INTEGERTV:
             ( *i_accumulator ) *= cell.payload.integer.value;
@@ -116,8 +234,10 @@ struct cons_pointer multiply_accumulate( struct cons_pointer arg,
             result = arg;
             break;
         default:
-            result = lisp_throw( c_string_to_lisp_string
+            result =
-                                 ( "Cannot multiply: not a number" ), frame );
+                lisp_throw
+                ( c_string_to_lisp_string
+                  ( "Cannot multiply: not a number" ), frame );
     }
     return result;
 }
@@ -128,27 +248,30 @@ struct cons_pointer multiply_accumulate( struct cons_pointer arg,
  * @param frame the stack frame.
  * @return a pointer to an integer or real.
  */
-struct cons_pointer
+struct cons_pointer lisp_multiply( struct
-lisp_multiply( struct stack_frame *frame, struct cons_pointer env ) {
+                                   stack_frame
+                                   *frame, struct
+                                   cons_pointer env ) {
     struct cons_pointer result = NIL;
     long int i_accumulator = 1;
     long double d_accumulator = 1;
     int is_int = true;
-
+    for ( int i = 0; i < args_in_frame && !nilp( frame->arg[i] )
-    for ( int i = 0;
+          && !exceptionp( result ); i++ ) {
-          i < args_in_frame && !nilp( frame->arg[i] ) && !exceptionp( result );
-          i++ ) {
         result =
-            multiply_accumulate( frame->arg[i], frame, &i_accumulator,
+            multiply_accumulate( frame->arg[i],
-                                 &d_accumulator, &is_int );
+                                 frame,
+                                 &i_accumulator, &d_accumulator, &is_int );
     }
 
     struct cons_pointer more = frame->more;
-
+    while ( consp( more )
-    while ( consp( more ) && !exceptionp( result ) ) {
+            && !exceptionp( result ) ) {
         result =
-            multiply_accumulate( c_car( more ), frame, &i_accumulator,
+            multiply_accumulate( c_car
-                                 &d_accumulator, &is_int );
+                                 ( more ),
+                                 frame,
+                                 &i_accumulator, &d_accumulator, &is_int );
         more = c_cdr( more );
     }
 
@@ -169,32 +292,37 @@ lisp_multiply( struct stack_frame *frame, struct cons_pointer env ) {
  * @param frame the stack frame.
  * @return a pointer to an integer or real.
  */
-struct cons_pointer
+struct cons_pointer lisp_subtract( struct
-lisp_subtract( struct stack_frame *frame, struct cons_pointer env ) {
+                                   stack_frame
+                                   *frame, struct
+                                   cons_pointer env ) {
     struct cons_pointer result = NIL;
-
     struct cons_space_object arg0 = pointer2cell( frame->arg[0] );
     struct cons_space_object arg1 = pointer2cell( frame->arg[1] );
-
+    if ( integerp( frame->arg[0] )
-    if ( integerp( frame->arg[0] ) && integerp( frame->arg[1] ) ) {
+         && integerp( frame->arg[1] ) ) {
         result =
-            make_integer( arg0.payload.integer.value -
+            make_integer( arg0.payload.integer.value
-                          arg1.payload.integer.value );
+                          - arg1.payload.integer.value );
-    } else if ( realp( frame->arg[0] ) && realp( frame->arg[1] ) ) {
+    } else if ( realp( frame->arg[0] )
+                && realp( frame->arg[1] ) ) {
         result =
             make_real( arg0.payload.real.value - arg1.payload.real.value );
-    } else if ( integerp( frame->arg[0] ) && realp( frame->arg[1] ) ) {
+    } else if ( integerp( frame->arg[0] )
+                && realp( frame->arg[1] ) ) {
         result =
-            make_real( numeric_value( frame->arg[0] ) -
+            make_real( numeric_value
-                       arg1.payload.real.value );
+                       ( frame->arg[0] ) - arg1.payload.real.value );
-    } else if ( realp( frame->arg[0] ) && integerp( frame->arg[1] ) ) {
+    } else if ( realp( frame->arg[0] )
+                && integerp( frame->arg[1] ) ) {
         result =
             make_real( arg0.payload.real.value -
                        numeric_value( frame->arg[1] ) );
     } else {
         /* TODO: throw an exception */
-        lisp_throw( c_string_to_lisp_string
+        lisp_throw
-                    ( "Cannot subtract: not a number" ), frame );
+            ( c_string_to_lisp_string
+              ( "Cannot subtract: not a number" ), frame );
     }
 
     // and if not nilp[frame->arg[2]) we also have an error.
@@ -208,29 +336,34 @@ lisp_subtract( struct stack_frame *frame, struct cons_pointer env ) {
  * @param frame the stack frame.
  * @return a pointer to an integer or real.
  */
-struct cons_pointer
+struct cons_pointer lisp_divide( struct
-lisp_divide( struct stack_frame *frame, struct cons_pointer env ) {
+                                 stack_frame
+                                 *frame, struct
+                                 cons_pointer env ) {
     struct cons_pointer result = NIL;
-
     struct cons_space_object arg0 = pointer2cell( frame->arg[0] );
     struct cons_space_object arg1 = pointer2cell( frame->arg[1] );
-
+    if ( numberp( frame->arg[1] )
-    if ( numberp( frame->arg[1] ) && numeric_value( frame->arg[1] ) == 0 ) {
+         && numeric_value( frame->arg[1] ) == 0 ) {
-        lisp_throw( c_string_to_lisp_string
+        lisp_throw
-                    ( "Cannot divide: divisor is zero" ), frame );
+            ( c_string_to_lisp_string
-    } else if ( numberp( frame->arg[0] ) && numberp( frame->arg[1] ) ) {
+              ( "Cannot divide: divisor is zero" ), frame );
-        long int i = ( long int ) numeric_value( frame->arg[0] ) /
+    } else if ( numberp( frame->arg[0] )
-            numeric_value( frame->arg[1] );
+                && numberp( frame->arg[1] ) ) {
-        long double r = ( long double ) numeric_value( frame->arg[0] ) /
+        long int i = ( long int )
-            numeric_value( frame->arg[1] );
+            numeric_value( frame->arg[0] ) / numeric_value( frame->arg[1] );
+        long double r = ( long double )
+            numeric_value( frame->arg[0] )
+            / numeric_value( frame->arg[1] );
         if ( fabsl( ( long double ) i - r ) < 0.0000000001 ) {
             result = make_integer( i );
         } else {
             result = make_real( r );
         }
     } else {
-        lisp_throw( c_string_to_lisp_string
+        lisp_throw
-                    ( "Cannot divide: not a number" ), frame );
+            ( c_string_to_lisp_string
+              ( "Cannot divide: not a number" ), frame );
     }
 
     return result;