Discover reviews on "testing newapplication" based on Reddit discussions and experiences.
Last updated: December 17, 2025 at 09:56 PM
Reddit Comments Summary on Testing New application
Implementing Functor and applicative
- Not every Functor is applicative, so implementing applicative cannot be a prerequisite for implementing Functor.
- Similarly, implementing applicative before Monad is not viable.
Deriving Functions from Monad Implementation
- It was suggested that all functions for Functor and applicative could be automatically derived from the Monad implementation.
- The use of
Wr[ap](https://www.amazon.com/AP-Biology-Premium-2026-Comprehensive/dp/150629670X/ref=sr_1_1?dib=eyJ2IjoiMSJ9.UiDe070j2sNoZqjsLcpPgnFsEIxqVcZPBiHMX_dMptjiBYw-8_9kXTX08hAvplRRo_8Yik2fl798H8SP8ceteNYVMyRZzcNeQayNeG-sxUeNOx6wQ10rTozFFXy5Ql1hf997HGqTueA3X1WTi79LTt5Xl6LyGbj6iz7xi6nTErFvfvh8e83QkNDi5anvZrn2QL0Wv0uNcoHCCX8P81jf-LOu2hNv8Xvt8tVTmemNKpE.3I8IwFgpKDn8E-aewO15462FP85KIDJQbkKpXJyuGZI&dib_tag=se&keywords=ap&qid=1766008610&sr=8-1&tag=redditrevie08-20)ped[Monad](https://www.amazon.com/Hieroglyphic-Monad-Dr-John-Dee/dp/157863203X/ref=sr_1_1?dib=eyJ2IjoiMSJ9.X_bAGr3M895dxvmzp4g6PqcueEWIg4GOU8mzNpCqegE5FRan43Rfq58rR0GgP4ADF1DdwID9aUs21NZaQ4ylDbrvdCd3jWZUUfXk5fM823wOHpEdd-lc9RE0nhHz0aVPKBjT32T9PnnfmUlilyL4y2hcEV3yelk6mpY-0C_Fjtluf_l9ZLW9ANfQ8uVx4LGgISuuEG_8ezNuiOoUiGg22kGLgDXzXUfxfnDVpGVNvzU.VHGunqxgK5EIv0xQ5eQ_y9QHHN7V52p4eCqKA0dGLHU&dib_tag=se&keywords=Monad&qid=1766008610&sr=8-1&tag=redditrevie08-20)was also mentioned for deriving Functor and applicative instances.
Alternative Implementations
- There was a code snippet provided for implementing applicative using
[ap](https://www.amazon.com/AP-Biology-Premium-2026-Comprehensive/dp/150629670X/ref=sr_1_1?dib=eyJ2IjoiMSJ9.UiDe070j2sNoZqjsLcpPgnFsEIxqVcZPBiHMX_dMptjiBYw-8_9kXTX08hAvplRRo_8Yik2fl798H8SP8ceteNYVMyRZzcNeQayNeG-sxUeNOx6wQ10rTozFFXy5Ql1hf997HGqTueA3X1WTi79LTt5Xl6LyGbj6iz7xi6nTErFvfvh8e83QkNDi5anvZrn2QL0Wv0uNcoHCCX8P81jf-LOu2hNv8Xvt8tVTmemNKpE.3I8IwFgpKDn8E-aewO15462FP85KIDJQbkKpXJyuGZI&dib_tag=se&keywords=ap&qid=1766008610&sr=8-1&tag=redditrevie08-20)and Monad using[>>=](https://www.amazon.com/Wicked-Bonus-Jon-M-Chu/dp/B0DGZV9Z5Z/ref=sr_1_1?dib=eyJ2IjoiMSJ9._ToIy9g6NY-8GZScD9RqlMZTvldAnhdQOS2SEql6y2pK2kBAaN44Lba3i5KWaVUE7z3378zEs6USJIsrwq0rAqnC2ipz1YcqlvDnLuh6E_59JWvyet1OqK5WXBdP8zqXQFcXa9hCDlrXYGNEozU636nZR4x2FABD7o1AM02h9a6Vtm19z-sVDTsrUZGE42UdLEYElYW5U5Xi6gSs4TLxUUPbtScvEDZsy14fnI_YW3E.w-qTY-5Hvd3Bg1BX_We4XUuwxbRCdGxgqqQQKnoTJBk&dib_tag=se&keywords=%3E%3E%3D&qid=1766008610&sr=8-1&tag=redditrevie08-20). - A comment highlighted that the use of
Derive[Functor](https://www.amazon.com/Green-Functors-G-sets-Lecture-Mathematics/dp/3540635505/ref=sr_1_1?dib=eyJ2IjoiMSJ9.9tX0yEyyXPY6NOEU43h-Jsb4DqzFlaiYiAcoRiSq87JMe-ndx6qjByC3v6-IWoE4fdMdwwwsBBm-_GJ0x3dFir1QMUrDpRt4u5N8jDT-q0v3zDYg-Bvz7QAEBtRu97jXeuDp0_vLmKEEm3NdAetp1ZaMhM9NOtVqveKUhxZrlNu8yVmFY0qG1ry9hd0NhSVlJy4qGLkJoTIL6z1HaXZEk_TOI4Da5Yg6zdtjO6I8OQSOspvZmb1v4tkOGeyCAlESe1wiuqP9r5WI9J65sb7Y-znPlhaCnNITnc77zVAOVGg.HNCuSHsmXyHBCM-rbvgX21EVJAhYCqQdTGDCldXsYyI&dib_tag=se&keywords=Functor&qid=1766008610&sr=8-1&tag=redditrevie08-20)for implementing Functor is slightly worse but acceptable.
Issues with Instance Declaration
- There was a caution about declaring
instance New[[ap](https://www.amazon.com/AP-Biology-Premium-2026-Comprehensive/dp/150629670X/ref=sr_1_1?dib=eyJ2IjoiMSJ9.UiDe070j2sNoZqjsLcpPgnFsEIxqVcZPBiHMX_dMptjiBYw-8_9kXTX08hAvplRRo_8Yik2fl798H8SP8ceteNYVMyRZzcNeQayNeG-sxUeNOx6wQ10rTozFFXy5Ql1hf997HGqTueA3X1WTi79LTt5Xl6LyGbj6iz7xi6nTErFvfvh8e83QkNDi5anvZrn2QL0Wv0uNcoHCCX8P81jf-LOu2hNv8Xvt8tVTmemNKpE.3I8IwFgpKDn8E-aewO15462FP85KIDJQbkKpXJyuGZI&dib_tag=se&keywords=ap&qid=1766008610&sr=8-1&tag=redditrevie08-20)plicative](https://www.amazon.com/Designs-Ultra-Standard-Experience-Partner-[ap](https://www.amazon.com/AP-Biology-Premium-2026-Comprehensive/dp/150629670X/ref=sr_1_1?dib=eyJ2IjoiMSJ9.UiDe070j2sNoZqjsLcpPgnFsEIxqVcZPBiHMX_dMptjiBYw-8_9kXTX08hAvplRRo_8Yik2fl798H8SP8ceteNYVMyRZzcNeQayNeG-sxUeNOx6wQ10rTozFFXy5Ql1hf997HGqTueA3X1WTi79LTt5Xl6LyGbj6iz7xi6nTErFvfvh8e83QkNDi5anvZrn2QL0Wv0uNcoHCCX8P81jf-LOu2hNv8Xvt8tVTmemNKpE.3I8IwFgpKDn8E-aewO15462FP85KIDJQbkKpXJyuGZI&dib_tag=se&keywords=ap&qid=1766008610&sr=8-1&tag=redditrevie08-20)plicative/dp/B0FFM8XKL8/ref=sr_1_1?dib=eyJ2IjoiMSJ9.pUSkdUuRVI9nVUeC2phUTV5iyn9gxOIz32aHsGs0UAl7W_W05_GozHI5cdYwN8AaWxZtwvxY_AWPZ7cW5nM7g3659h4OVwZ7yMQYfWpnhUn9EU0Xp9dIQSOCJTO-cR8SpA[ap](https://www.amazon.com/AP-Biology-Premium-2026-Comprehensive/dp/150629670X/ref=sr_1_1?dib=eyJ2IjoiMSJ9.UiDe070j2sNoZqjsLcpPgnFsEIxqVcZPBiHMX_dMptjiBYw-8_9kXTX08hAvplRRo_8Yik2fl798H8SP8ceteNYVMyRZzcNeQayNeG-sxUeNOx6wQ10rTozFFXy5Ql1hf997HGqTueA3X1WTi79LTt5Xl6LyGbj6iz7xi6nTErFvfvh8e83QkNDi5anvZrn2QL0Wv0uNcoHCCX8P81jf-LOu2hNv8Xvt8tVTmemNKpE.3I8IwFgpKDn8E-aewO15462FP85KIDJQbkKpXJyuGZI&dib_tag=se&keywords=ap&qid=1766008610&sr=8-1&tag=redditrevie08-20)zOzxRvxzAWJZSsR2vJ1oc1rhNtKJBoIiI_CBywPHJSyTAzf8tjJwGYT63K1zXAZ-YB2TD84aJ1EaTDCgsZC8dOl2hXM_NmT2oUh0Aik.rPh2GdmHkSZ-NRA5GZamRNOaQ2mNKLgf7UYLSWbrKWs&dib_tag=se&keywords=[ap](https://www.amazon.com/AP-Biology-Premium-2026-Comprehensive/dp/150629670X/ref=sr_1_1?dib=eyJ2IjoiMSJ9.UiDe070j2sNoZqjsLcpPgnFsEIxqVcZPBiHMX_dMptjiBYw-8_9kXTX08hAvplRRo_8Yik2fl798H8SP8ceteNYVMyRZzcNeQayNeG-sxUeNOx6wQ10rTozFFXy5Ql1hf997HGqTueA3X1WTi79LTt5Xl6LyGbj6iz7xi6nTErFvfvh8e83QkNDi5anvZrn2QL0Wv0uNcoHCCX8P81jf-LOu2hNv8Xvt8tVTmemNKpE.3I8IwFgpKDn8E-aewO15462FP85KIDJQbkKpXJyuGZI&dib_tag=se&keywords=ap&qid=1766008610&sr=8-1&tag=redditrevie08-20)plicative&qid=1766008610&sr=8-1&tag=redditrevie08-20) f => New[Functor](https://www.amazon.com/Green-Functors-G-sets-Lecture-Mathematics/dp/3540635505/ref=sr_1_1?dib=eyJ2IjoiMSJ9.9tX0yEyyXPY6NOEU43h-Jsb4DqzFlaiYiAcoRiSq87JMe-ndx6qjByC3v6-IWoE4fdMdwwwsBBm-_GJ0x3dFir1QMUrDpRt4u5N8jDT-q0v3zDYg-Bvz7QAEBtRu97jXeuDp0_vLmKEEm3NdAetp1ZaMhM9NOtVqveKUhxZrlNu8yVmFY0qG1ry9hd0NhSVlJy4qGLkJoTIL6z1HaXZEk_TOI4Da5Yg6zdtjO6I8OQSOspvZmb1v4tkOGeyCAlESe1wiuqP9r5WI9J65sb7Y-znPlhaCnNITnc77zVAOVGg.HNCuSHsmXyHBCM-rbvgX21EVJAhYCqQdTGDCldXsYyI&dib_tag=se&keywords=Functor&qid=1766008610&sr=8-1&tag=redditrevie08-20) f. - Mention was made of potential errors due to overlapping instances when implementing other instances for
New[Functor](https://www.amazon.com/Green-Functors-G-sets-Lecture-Mathematics/dp/3540635505/ref=sr_1_1?dib=eyJ2IjoiMSJ9.9tX0yEyyXPY6NOEU43h-Jsb4DqzFlaiYiAcoRiSq87JMe-ndx6qjByC3v6-IWoE4fdMdwwwsBBm-_GJ0x3dFir1QMUrDpRt4u5N8jDT-q0v3zDYg-Bvz7QAEBtRu97jXeuDp0_vLmKEEm3NdAetp1ZaMhM9NOtVqveKUhxZrlNu8yVmFY0qG1ry9hd0NhSVlJy4qGLkJoTIL6z1HaXZEk_TOI4Da5Yg6zdtjO6I8OQSOspvZmb1v4tkOGeyCAlESe1wiuqP9r5WI9J65sb7Y-znPlhaCnNITnc77zVAOVGg.HNCuSHsmXyHBCM-rbvgX21EVJAhYCqQdTGDCldXsYyI&dib_tag=se&keywords=Functor&qid=1766008610&sr=8-1&tag=redditrevie08-20). - It was noted that such a declaration might not be valid Haskell without any extensions.
General Advice
- A warning against doing Category Theory in Haskell was given, advising against it to avoid disappointment.
