Hi, I've been wondering what is essential to Haskell and what isn't. Not from a point of view of what could be removed from the language, but what could be removed from a Core language. Given the features of higher-order, laziness and data types: Laziness can be converted to higher-order functions Data types can be converted to higher-order functions Higher-order functions can be converted to Data So as far as I can see it we have left: {data-types only} {higher-order functions only} But we don't have laziness only, so my question is if it is possible to represent all of Haskell in a first-order language without data types, but with laziness. If its possible to do so in a strict first-order language without data types, then I'd also be interested. Are any of these known results? Thanks Neil References: * data types -> higher order is in "Efficient Interpretation by Transforming Data Types and Patterns to Functions" http://www.cs.nott.ac.uk/~nhn/TFP2006/Papers/03-JansenKoopmanPlasmeijer-Effi... * laziness -> functions, functions -> data is in "Definitional Interpreters for Higher-Order Programming Languages" http://www.brics.dk/~hosc/local/HOSC-11-4-pp363-397.pdf