feat: adds example for calculator

2 files changed, 52 insertions, 2 deletions

diff --git a/src/eval.ts b/src/eval.ts
index 87bcd6d..84ab52f 100644
--- a/src/eval.ts
+++ b/src/eval.ts
@@ -371,10 +371,59 @@ const getFunctions = (
       return EvalValue.Number(result)
     },
 
+    // TODO: Structural comparison?
+    equals: async () =>
+      compare(
+        args[0],
+        args[1],
+        actions,
+        (a, b) => evalValueToString(a) === evalValueToString(b),
+      ),
+
+    gt: async () =>
+      compare(
+        args[0],
+        args[1],
+        actions,
+        (a, b) => (evalValueToNumber(a) ?? 0) > (evalValueToNumber(b) ?? 0),
+      ),
+
+    lt: async () =>
+      compare(
+        args[0],
+        args[1],
+        actions,
+        (a, b) => (evalValueToNumber(a) ?? 0) < (evalValueToNumber(b) ?? 0),
+      ),
+
+    gte: async () =>
+      compare(
+        args[0],
+        args[1],
+        actions,
+        (a, b) => (evalValueToNumber(a) ?? 0) >= (evalValueToNumber(b) ?? 0),
+      ),
+
+    lte: async () =>
+      compare(
+        args[0],
+        args[1],
+        actions,
+        (a, b) => (evalValueToNumber(a) ?? 0) <= (evalValueToNumber(b) ?? 0),
+      ),
+
     _: () => Promise.reject(new Error(`Not implemented: ${name}`)),
   })
 }
 
+export const compare = async (
+  a: Expr,
+  b: Expr,
+  actions: EvalActions,
+  cmp: (a: EvalValue, b: EvalValue) => boolean,
+) =>
+  EvalValue.Boolean(cmp(await evalExpr(a, actions), await evalExpr(b, actions)))
+
 const evalBinOp = async (
   left: Expr,
   right: Expr,
@@ -401,7 +450,8 @@ export const evalCalcExpr = (
       }),
     Parens: ({ expr }) => evalCalcExpr(expr, actions),
     _: async () => {
-      if (expr.tag === 'Call' && expr.value.name === 'var') {
+      // Special expressions to double-evaluate
+      if (expr.tag === 'Call' && ['var', 'get-var'].includes(expr.value.name)) {
         const value = await evalExprAsString(expr, actions)
         try {
           const pvalue = await evalExpr(parseExpr(value ?? ''), actions)
diff --git a/src/parser.ts b/src/parser.ts
index 81f7a9e..928fc00 100644
--- a/src/parser.ts
+++ b/src/parser.ts
@@ -116,7 +116,7 @@ const precedence = (op: BinOp) =>
     _: () => -1,
   })
 
-const binOpWithFixitySwitchity = (op: BinOp, left: Expr, right: Expr) =>
+const binOpWithFixitySwitchity = (op: BinOp, left: Expr, right: Expr): Expr =>
   match(right, {
     BinOp: binOp => {
       if (precedence(op) >= precedence(binOp.op)) {