1
0
forked from GitHub/gf-core

Transfer reference: added list patterns, do notation.

This commit is contained in:
bringert
2005-12-07 10:03:18 +00:00
parent 0dfd8c1517
commit 5c06d7279c
2 changed files with 153 additions and 47 deletions

View File

@@ -61,6 +61,7 @@ braces and semicolons. Thus the above is equivalent to:
case x of { p1 -> e1 ; p2 -> e2 }
```
== Imports ==
A Transfer module start with some imports. Most modules will have to
@@ -89,11 +90,13 @@ equations. The first equation whose patterns match the function arguments
is used when the function is called. Pattern equations are on the form:
```
f p1 ... p1n = exp
f p11 ... p1m = exp
...
f qn1 ... qnm = exp
f pn1 ... pnm = exp
```
where ``p11`` to ``pnm`` are patterns, see [Patterns #patterns].
== Data type declarations ==
@@ -137,7 +140,6 @@ let x1 : T1 = exp1
```
== Types ==
=== Function types ===[function_types]
@@ -182,7 +184,8 @@ in the type. Such dependent function types are written:
```
Here, ``x1`` can be used in ``T2`` to ``Tn``, ``x1`` can be used
in ``T2`` to ``Tn``
in ``T2`` to ``Tn``.
=== Basic types ===
@@ -191,12 +194,14 @@ in ``T2`` to ``Tn``
The type of integers is called ``Integer``.
standard decmial integer literals are used to represent values of this type.
==== Floating-point numbers ====
The only currently supported floating-point type is ``Double``, which supports
IEEE-754 double-precision floating-point numbers. Double literals are written
in decimal notation, e.g. ``123.456``.
==== Strings ====
There is a primitive ``String`` type. This might be replaced by a list of
@@ -255,12 +260,14 @@ rec p1 = exp1
pn = expn
```
==== Record subtyping ====
A record of some type R1 can be used as a record of any type R2
such that for every field ``p1 : T1`` in R2, ``p1 : T1`` is also a
field of T1.
=== Tuples ===
Tuples on the form:
@@ -293,7 +300,7 @@ be used instead of ``Cons``. These are just syntactic sugar for expressions
using ``Nil`` and ``Cons``, with the type arguments hidden.
== Pattern matching ==
== Case expressions ==
Pattern matching is done in pattern equations and by using the
``case`` construct:
@@ -305,6 +312,7 @@ case exp of
pn | guardn -> rhsn
```
where ``p1`` to ``pn`` are patterns, see [Patterns #patterns].
``guard1`` to ``guardn`` are boolean expressions. Case arms can also be written
without guards, such as:
@@ -318,7 +326,8 @@ This is the same as writing:
pk | True -> rhsk
```
The syntax of patterns are decribed below.
== Patterns ==[patterns]
=== Constructor patterns ===
@@ -386,6 +395,32 @@ FIXME: talk about how this is expanded
=== List patterns ===
When pattern matching in lists, there are two special constructs.
A whole list can be matched be a list of patterns:
```
[p1, ... , pn]
```
This pattern will match lists of length n, such that each element
in the list matches the corresponding pattern. The empty list pattern:
```
[]
```
is a special case of this. It matches the empty list, oddly enough.
Non-empty lists can also be matched with ``::``-patterns:
```
p1::p2
```
This pattern matches a non-empty lists such that the first element of
the list matches ``p1`` and the rest of the list matches ``p2``.
=== Tuple patterns ===
Tuples patterns on the form:
@@ -418,14 +453,35 @@ A metavariable is a way to the the Transfer type checker that:
"you should be able to figure out what this should be,
I can't be bothered to tell you".
Metavariables can be used to avoid having to give type variables
and dictionaries explicitly.
Metavariables can be used to avoid having to give type
and dictionary arguments explicitly.
== Overloaded functions / Type classes ==
== Operators ==
== Compositional functions ==
== do notation ==
Sequences of operations in the Monad type class can be written
using do-notation, like in Haskell:
```
do x <- f
y <- g x
h y
```
is equivalent to:
```
f >>= \x -> g x >>= \y -> h y
```