diff --git a/src/external.d.ts b/src/external.d.ts
index 60b149d..ceaf6da 100644
--- a/src/external.d.ts
+++ b/src/external.d.ts
@@ -7,7 +7,7 @@ declare module 'interval-arithmetic-eval' {
   export class Interval {
     lo: number
     hi: number
-
+    constructor(lo: number | Interval, hi?: number)
     static isEmpty(n: Interval | number): boolean
     static isWhole(n: Interval | number): boolean
     static intervalsOverlap(n: Interval, r: Interval): boolean
diff --git a/src/samplers/builtIn.ts b/src/samplers/builtIn.ts
index 730b155..39ddd87 100644
--- a/src/samplers/builtIn.ts
+++ b/src/samplers/builtIn.ts
@@ -1,5 +1,5 @@
 import { linspace, sgn, infinity, clamp, space, isValidNumber } from '../utils.mjs'
-import { builtIn as evaluate } from './eval.mjs'
+import { builtIn as builtInEvaluate } from './eval.mjs'
 
 import type { FunctionPlotDatum, FunctionPlotScale, PointFunction, VectorFunction } from '../types.js'
 import type { SamplerParams, SamplerFn, BuiltInSamplerResult, BuiltInSamplerResultGroup } from './types.js'
@@ -27,7 +27,7 @@ function checkAsymptote(
   let oldY: number, oldX: number
   for (let i = 0; i < n; i += 1) {
     const x = samples[i]
-    const y = evaluate(d, 'fn', { x })
+    const y = builtInEvaluate(d, 'fn', { x })
 
     if (oldY) {
       const deltaY = y - oldY
@@ -122,7 +122,7 @@ function linear(samplerParams: SamplerParams): BuiltInSamplerResult {
   const data: Array<[number, number]> = []
   for (let i = 0; i < allX.length; i += 1) {
     const x = allX[i]
-    let y = evaluate(samplerParams.d, 'fn', { x })
+    let y = builtInEvaluate(samplerParams.d, 'fn', { x })
     if (isValidNumber(x) && isValidNumber(y)) {
       y = clamp(y, yMin, yMax)
       data.push([x, y])
@@ -140,8 +140,8 @@ function parametric(samplerParams: SamplerParams): BuiltInSamplerResult {
   const samples: BuiltInSamplerResultGroup = []
   for (let i = 0; i < tCoords.length; i += 1) {
     const t = tCoords[i]
-    const x = evaluate(samplerParams.d, 'x', { t })
-    const y = evaluate(samplerParams.d, 'y', { t })
+    const x = builtInEvaluate(samplerParams.d, 'x', { t })
+    const y = builtInEvaluate(samplerParams.d, 'y', { t })
     samples.push([x, y])
   }
   return [samples]
@@ -155,7 +155,7 @@ function polar(samplerParams: SamplerParams): BuiltInSamplerResult {
   const samples: BuiltInSamplerResultGroup = []
   for (let i = 0; i < thetaSamples.length; i += 1) {
     const theta = thetaSamples[i]
-    const r = evaluate(samplerParams.d, 'r', { theta })
+    const r = builtInEvaluate(samplerParams.d, 'r', { theta })
     const x = r * Math.cos(theta)
     const y = r * Math.sin(theta)
     samples.push([x, y])
diff --git a/src/samplers/interval.ts b/src/samplers/interval.ts
index 84bb1a6..7c4cbcc 100644
--- a/src/samplers/interval.ts
+++ b/src/samplers/interval.ts
@@ -1,6 +1,6 @@
 import intervalArithmeticEval, { Interval } from 'interval-arithmetic-eval'
 
-import { interval as evaluate } from './eval.mjs'
+import { interval as intervalEvaluate, builtIn as builtInEvaluate } from './eval.mjs'
 import { infinity, space, interval2dTypedArray } from '../utils.mjs'
 import globals from '../globals.mjs'
 
@@ -125,7 +125,7 @@ function interval1d({ d, xAxis, range, nSamples, xScale, yScale }: SamplerParams
   const samples: IntervalSamplerResultGroup = []
   for (let i = 0; i < xCoords.length - 1; i += 1) {
     const x = { lo: xCoords[i], hi: xCoords[i + 1] }
-    const y = evaluate(d, 'fn', { x })
+    const y = intervalEvaluate(d, 'fn', { x })
     if (!Interval.isEmpty(y) && !Interval.isWhole(y)) {
       samples.push([x, y])
     }
@@ -179,7 +179,7 @@ function smallRect(x: Interval, _: Interval) {
 }
 
 function quadTree(x: Interval, y: Interval, d: FunctionPlotDatum) {
-  const sample = evaluate(d, 'fn', { x, y })
+  const sample = intervalEvaluate(d, 'fn', { x, y })
   const fulfills = Interval.zeroIn(sample)
   if (!fulfills) {
     return this