[math] Better error for 2 + 2 4

This now reports "TOO_MANY_ARGS" instead of no error (and triggering
an assertion).

We might want to add a new error type or report the missing operator
before, but this is okay for now.

src/tinyexpr.c

@@ -50,7 +50,7 @@ typedef struct state {
 
     const te_variable *lookup;
     int lookup_len;
-    int error;
+    te_error_type_t error;
 } state;
 
 
@@ -502,6 +502,7 @@ te_expr *te_compile(const char *expression, const te_variable *variables, int va
     s.start = s.next = expression;
     s.lookup = variables;
     s.lookup_len = var_count;
+    s.error = TE_ERROR_NONE;
 
     next_token(&s);
     te_expr *root = expr(&s);
@@ -510,7 +511,17 @@ te_expr *te_compile(const char *expression, const te_variable *variables, int va
         te_free(root);
         if (error) {
             error->position = (s.next - s.start) + 1;
-            error->type = s.error;
+            if (s.error != TE_ERROR_NONE) {
+                error->type = s.error;
+            } else {
+                // If we're not at the end but there's no error, then that means we have a superfluous
+                // token that we have no idea what to do with.
+                // This occurs in e.g. `2 + 2 4` - the "4" is just not part of the expression.
+                // We can report either "too many arguments" or "expected operator", but the operator
+                // should be reported between the "2" and the "4".
+                // So we report TOO_MANY_ARGS on the "4".
+                error->type = TE_ERROR_TOO_MANY_ARGS;
+            }
         }
         return 0;
     } else {

src/tinyexpr.h

@@ -33,7 +33,7 @@ extern "C" {
 #endif
 
 
-    enum {
+    typedef enum {
         TE_ERROR_NONE = 0,
         TE_ERROR_UNKNOWN_VARIABLE = 1,
         TE_ERROR_MISSING_CLOSING_PAREN = 2,
@@ -42,9 +42,7 @@ extern "C" {
         TE_ERROR_TOO_MANY_ARGS = 5,
         TE_ERROR_MISSING_OPERATOR = 6,
         TE_ERROR_UNKNOWN = 7
-    };
-    typedef int te_error_type_t;
-
+    } te_error_type_t;
 
 
     typedef struct te_error_t {

tests/math.err

@@ -19,3 +19,6 @@ math: Error: Expression is bogus
 math: Error: Too few arguments
 'sin()'
      ^
+math: Error: Too many arguments
+'2 + 2 4'
+       ^

tests/math.in

@@ -28,3 +28,4 @@ not math '2 - '
 not math 'ncr(1)'
 not math 'max()'
 not math 'sin()'
+not math '2 + 2 4'