Discussion on Commands

Published by cce on 2011-07-26

In HTSQL, we’d like commands and functions to have the same syntax. How do we make this work?


Currently formatters are handled as a special case, for example, /school/:csv. We’d like this to be equivalent (using postfix syntax) to /csv(/school). Broadly speaking, we’d like commands to have same syntax as functions. The challenge here is how to get from the internal syntax tree to the WSGI output. Is binding different? What are the other translation phases to get to the formatted output.

Our previous approach (in 1.x) had a separate syntax for commands and each command was responsible for translating it’s arguments into an output. We had command chaining via typed pipeline. Commands had input/output interface with a set of types: SYNTAX (a syntax tree), PRODUCT (tabular output of an SQL query), RENDER (WSGI output), among others.

In this version, we need a pipeline support, but we should assume that they would be supported by nested commands. For example, suppose we have a /meta() command that executes its argument on the meta-data structure for the current context. Hence, /html(/meta(/column)) would produce an HTML formatted table listing columns currently available to the current user. This query could also be written in postfix syntax as /column/:meta/:html.

So what happens after a syntax tree? What is the result of the translation and how do we convert this to final output.

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