README
¶
Morel
A functional query language, implemented in Go.
Morel is Standard ML with relational extensions: a from expression
that queries collections the way SQL queries tables, but inside a
language that has lambdas, polymorphism and pattern-matching.
Requirements
Go version 1.25 or higher.
Get Morel
Install
$ go install github.com/hydromatic/morel-go/cmd/morel@latest
This puts a morel binary in $(go env GOPATH)/bin.
Download and build
$ git clone git://github.com/hydromatic/morel-go.git
$ cd morel-go
$ go build ./cmd/morel; ./morel
Run the shell
$ ./morel
morel-go v0.8.0 (go1.26.5, darwin/arm64)
- "Hello, world!";
val it = "Hello, world!" : string
Type control+D to exit the shell.
Within the shell, the use function reads and evaluates source from a
file:
- use "script.sml";
For quick testing, use the -e flag.
$ ./morel -e "1 + 2"
val it = 3 : int
$ ./morel -e "from i in [1,2,3] where i > 1"
val it = [2,3] : int list
$ ./morel -e 'let fun double x = x * 2 in map double [2,3,4] end'
val it = [4,6,8] : int list
Named files are run as scripts; a file argument of - means standard
input. Run ./morel --help for the full list of options.
Documentation
Morel Go does not yet have documentation of its own; the language it implements is the one described by Morel Java.
- Morel Java language reference
- Query reference
- Datalog support
- "How to" guide
- Change log
- Reading test scripts can be instructive; try, for example, relational.smli or built-in.smli
Status
Morel Go aims to be compatible with the Morel language as implemented
by Morel Java, and its strategy
is to copy that project's .smli test scripts and get them to pass.
Compatibility is therefore measured by how much of Morel Java's script
corpus Morel Go reproduces line for line: currently about 87%. (See
"Morel on Go"
for how the port was done.)
Implemented:
- Literals, variables, and comments
let,val(includingval rec),fun,fn, and function applicationif,case, and pattern-matching over constants, wildcards, tuples, records, and lists- Type inference (Hindley-Milner) and type variables
- Primitive, function, list, bag, tuple, record, and vector types
datatypeandtypedeclarationsraise, and the built-in exceptions- Relational expressions:
from,join(includingleft,rightandfullouter joins),where,group,compute,order,skip,take,yield,yieldAllandinto - Datalog
- The standard library: 460 members in 25 structures, based on the
Standard ML Basis Library
and extended with
Bag,Datalog,Interact,Range,Relational,SysandVariant - A shell that reads scripts or standard input, evaluates a single
expression with
-e, and checks a script against its expected output in.smli(idempotent) format
Not implemented:
exceptiondeclarations, andhandlestructure,struct,signature,sig,openlocalwhile- References, and operators
!and:= - User-defined operators (
infix,infixr) - Overloaded functions (
over,val inst); they parse, but do not compile - External data: reading from the file system, or from a database via ODBC or JDBC
- Attributes (
[@ ... ]) and quoted identifiers - Command-line editing and history in the shell; there is no up-arrow recall, and nothing is saved between sessions
See also GitHub issues.
More information
- License: Apache License, Version 2.0
- Author: Julian Hyde (@julianhyde)
- Blog: http://blog.hydromatic.net
- Source code: https://github.com/hydromatic/morel-go
- Issues: https://github.com/hydromatic/morel-go/issues
- Change log and release notes
Documentation
¶
Overview ¶
Package morel is the root of morel-go, an interpreter for Morel, a functional query language. The implementation lives under internal/; the command lives under cmd/morel.
Source Files
Directories
¶
| Path | Synopsis |
|---|---|
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cmd
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morel
command
Command morel is an interpreter for Morel, a functional query language.
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Command morel is an interpreter for Morel, a functional query language. |
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internal
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ast
Package ast defines the abstract syntax tree that the parser produces: the user-facing representation, with source spans, before type resolution converts it to Core.
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Package ast defines the abstract syntax tree that the parser produces: the user-facing representation, with source spans, before type resolution converts it to Core. |
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compile
Package compile turns the AST into the typed Core IR: the TypeResolver deduces a type for every node by unification, and the Resolver converts the AST to Core using those types.
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Package compile turns the AST into the typed Core IR: the TypeResolver deduces a type for every node by unification, and the Resolver converts the AST to Core using those types. |
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core
Package core defines Morel's typed intermediate representation.
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Package core defines Morel's typed intermediate representation. |
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datalog
Package datalog implements the Souffle-flavored Datalog dialect behind the Datalog built-in structure: a parser, an analyzer (declarations, rule safety, stratification), and a translator that emits Morel source whose recursion is a Relational.iterate fixpoint.
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Package datalog implements the Souffle-flavored Datalog dialect behind the Datalog built-in structure: a parser, an analyzer (declarations, rule safety, stratification), and a translator that emits Morel source whose recursion is a Relational.iterate fixpoint. |
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eval
Package eval holds runtime values and the built-in functions.
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Package eval holds runtime values and the built-in functions. |
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parse
Package parse holds the Morel lexer and parser.
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Package parse holds the Morel lexer and parser. |
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pp
Package pp is a pretty-printer that lays out a document within a line-width limit.
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Package pp is a pretty-printer that lays out a document within a line-width limit. |
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shell
Package shell contains the kernel, the script runner, and the statement splitter.
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Package shell contains the kernel, the script runner, and the statement splitter. |
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sig
Package sig reads the subset of the built-in library's signature files (lib/*.sig) that gives the types of built-in values.
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Package sig reads the subset of the built-in library's signature files (lib/*.sig) that gives the types of built-in values. |
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token
Package token defines the lexical tokens of Morel and their source positions.
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Package token defines the lexical tokens of Morel and their source positions. |
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types
Package types defines Morel's types and the system that interns them.
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Package types defines Morel's types and the system that interns them. |
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unify
Package unify implements the Martelli-Montanari unification algorithm, with action hooks that fire as variables resolve and constraints that model overloaded operators.
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Package unify implements the Martelli-Montanari unification algorithm, with action hooks that fire as variables resolve and constraints that model overloaded operators. |
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Package lib embeds the built-in library sources: the signatures (*.sig), which give the types of the built-ins, and the Morel sources (*.sml) that define the derivable members of some structures.
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Package lib embeds the built-in library sources: the signatures (*.sig), which give the types of the built-ins, and the Morel sources (*.sml) that define the derivable members of some structures. |
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