2 files changed, 52 insertions, 1 deletions
diff --git a/src/arithm.c b/src/arithm.c
new file mode 100644
index 0000000..3f1e781
--- /dev/null
+++ b/src/arithm.c
@@ -0,0 +1,51 @@
+#include <stdlib.h>
+#include "syntax.h"
+#include "utils.h"
+
+
+int parse_num(char* str) {
+    // TODO: switch to dedicated Result type later
+    // TODO: add other bases (per bash arithmetic syntax)
+    char* endptr;
+    long n = strtol(str, &endptr, 10);
+    if (*endptr == '\0') {
+        return (int)n;
+    } else {
+        exit(42);
+    }
+}
+
+
+int eval_binop(BinOp op, int left, int right) {
+    switch (op) {
+        case PLUS:
+            return left+right;
+        case MULT:
+            return left*right;
+        default:
+            exit(99);
+    }
+}
+
+int eval_arithm_node(ArithmNode node, ShellState* shstate) {
+    char* num_str;
+    int left_val, right_val;
+
+    switch (node.kind) {
+        case ARITHM_INT_LIT:
+            return node.as.lit_val;
+        case ARITHM_VAR:
+            num_str = get_var(node.as.varname, shstate);
+            return parse_num(num_str);
+        case ARITHM_BINOP:
+            left_val = eval_arithm_node(*node.as.binop.left, shstate);
+            right_val = eval_arithm_node(*node.as.binop.right, shstate);
+            return eval_binop(node.as.binop.op, left_val, right_val); 
+    }
+}
+
+
+int eval_arithm_ast(ArithmAst ast, ShellState* shstate) {
+    // TODO: clean up the tree
+    return eval_arithm_node(*ast.root, shstate);
+}
diff --git a/src/syntax.h b/src/syntax.h
index 0b5396c..9b34818 100644
--- a/src/syntax.h
+++ b/src/syntax.h
@@ -23,7 +23,7 @@ struct ArithmNode {
     ArithmNodeKind kind;
     union {
         int lit_val;
-        IntVec open_fds;
+        char* varname;
         struct {
             BinOp op;
             ArithmNode* left;